The Preppy is the best for first timers. Platinum nibs are conistent and the cartridge/converter system is the most veritile of all the filling systems. It's a good baseline to gauge what you prefer.
I just can't recommend springing for the converter though. Platinum converters cost more than the Preppy. Their cartridges are sturdy and can be reused if you clean them out. I recommend picking up a blunt tipped syringe and refilling them with ink samples or from bottles.
Oh there are so many! Just pick a color or shade and there will be dozens that people swear by. Just be careful with shimmer inks since they can clog up the feed. They're fun and pretty but need a little attention.
I recommend checking out a few ink review blogs to find a handful to try. "Mountain in Ink" and "Fountain Pen Pharmacist" are two I follow. Places like Goulet Pens and Pen Chalet sell 4 mL samples for a few dollars which can last you a while on their own. Which is a great alternative to spending anywhere between $8-$60 for a bottle of ink.
As far as specifics: you can't go wrong with the Pilot Iroshizuku line, Diamine inks is another good one, and I think Sailor makes a lot of really nice ones.
Also from someone relatively new to fountain pens here are my paper observations:
Flexbook Adventure Notebook - 85gsm paper - Found to be very fountain pen friendly and tends to suck ink into the paper making it dry quickly making it good for fast writing with minimal to no bleed through.
Leuchtturm 1917 - 80gsm paper - Nice to write on but ink is slow to dry and dark in bleeds through (lighter inks may not be as noticeable).
Moleskine - 70gsm paper - Not recommended for fountain pens, the paper bleeds through if you even breath near it, feels scratchy while writing and can cause feathering with certain inks. The paper would be good for pencils though.
Rhodia - 80gsm paper - Nice paper to write on, has a slight scratchy texture that feels strange when first using it but you get used. Barely any bleed through with dark ink and dries pretty quickly.
R by Rhodia - 90gsm paper - This is their premium paper and although it has the same features as the normal Rhodia 80gsm paper if you can get this version I recommend it.
Midori - ??gsm paper - Haven't tried this paper yet.
The line is actually quite fine, it ends up being very economical on ink since it doesn't really dry out if you keep it closed. The plastic is decent quality. The cap isn't the most robust but if you're not rough the clip doesn't break.
The writing experience is good out of the box usually. Maybe a bit scratchy in your opinion but if you have flow issues the nib probably has misaligned tines.
Refilling cartridges from a bottle with a blunt tip syringe seems obvious to me but I have a lot of ink and don't write enough on the go to need several cartridge pens, I only have one with a box of cartridges that have little rubber stoppers. If you're crafty you can make your own from bigger gaskets or stoppers.
Platinum ink in cartridges is fine, just very expensive per litre.
IMHO, the Preppy is a pretty damn good pen - hardly my favorite but definitely a step up from the box of disposable Pilots I started experimenting with.
Converters / cartridges add a bit to the cost but aren’t terribly priced for the most part.
They’re far from perfect, but unlikely to disappoint entirely. Paired with decent paper (a vote for Clairefontaine as a daily driver here) they’re a good opener.
But don’t forget the Sport and Safari lines - they’re not quite as cheap but definitely not expensive. If you’re not a fan of pocket pens, the Perkeo can be had for $15 or so and i happen to prefer their converters/cartridges over Platinum’s.
They don't require it, but cheap paper sometimes doesn't play well with the water-based inks that fountain pens use and you get feathering (ink running down paper fibers and making your lines look blurry) or ink bleeding through the page. That being said, Japanese fine/extra fine like you're looking at normally lay down a thin enough line that there's no problem, my pilot kakuno never feathers even on the cheapest/worst paper
https://infosec.pub/u/niucllos@lemm.ee nailed it pretty well. I'd add though that unless you live in a major enough city to have a dedicated shop, it's probably worth picking up good paper online. Otherwise, your choices are largely 'fair-to-middling' and nowhere near the 'good' side of the spectrum.
Both weight (grams / sq meter usually) and coating matter - YMMV of course, all about your preferences and what's the most fun.
I'm sure that one can get decent paper in letter/legal - but the system most of the rest of the world uses makes a whole bunch of sense to me because the aspect ratio stays the same, each successively smaller size is just the size above it, rotated, then folded in half. A4 is analagous to letter, a5 is exactly one-half that and so on in both directions.
Edit: You won't go wrong with Marumann notebooks for "inexpensive paper that's well-bound and easily detachable" but... I've only been able to find them via Amazon in Japanese sizes that bear no connection with either the North American system or the rest of the world. They do, however, have a similar but inconsistent system for format naming. JIS B6 is sort of between A4 and A5, and feels downright alien in comparison with letter.
I think I will echo everyone else. A Platinum Preppy fine will be a great choice for a first time fountain pen user to decide whether a FP is right for them. $6 is not a big loss if it turns out you don't like it. It seals incredibly well and the pen can last a long time if you aren't too rough with it. It's definitely not a pen you can throw at the bottom of a backpack then toss the bag around (compare to the Lamy Safari which can take a good bit more abuse.).
The fine might be a touch scratchier since a Japanese F is usually more like a western EF. If you using a lot of garbage paper, definitely go with the EF. If you're working with paper that's more liquid ink friendly, maybe consider M for a slightly smoother experience.
Definitely buy a bunch of samples and a blunt tipped needle to fill the cartridge that comes with it in that order. If you aren't sure about 100% committing to FPs in that order, fill the rest of your cart for free shipping with stuff you could use otherwise. In terms of paper, I would say Rhodia and Clairefontaine are decent budget friendly paper. I am told Clairefontaine is dirt cheap in France. If you're in the UK, I'm also told Optik paper from Oxford is widely available for a good price there. Maybe consider some pens or pencils if the retailer has them.
Saw that my local pen shop started carrying PP pens.
So bowing to peer pressure I brought a black EF along with some other goodies.
I say that EF nib for me does not write nicely on fountain pen friendly paper, it tends to slide around on the paper ending up making a scribble instead of words.
Not sure if this is down to the amount of pressure I put on the pen or if the pen I got is an outlier.
Might have to go back and get another with a fine nib.
Thanks for the feedback. I bought a fine nib version since I made the post and I have been using it on a regular graph composition notebook and I see that it bleeds through and has a lot of ghosting. I have no reference for how a fountain pen could write so I guess its alright as far as feel goes. I did order a notebook made by Midori from Amazon. It will be my first experience with a higher quality paper with the Preppy.