Seriously considering pawning a kidney and joining the hobby. Questions!

If you are worried about budget and you can't just 3D print an army, I'd say orks are a lot more forgiving. There is a lot of 3rd party ork stuff, and since their aesthetic is ramshackle, it is quite easy to build ork tanks, walkers, vehicles, and artillery essentially from scratch.

Now, all of that assumes you don't care to participate in official GW tournaments, which are unfortunately quite strict on the policy of only using official GW figures. I think that is a far too constrictive and greedy policy, especially given how much in the past GW encouraged scratchbuilding and conversions. If you are playing with friends or an an independently run store, using 3rd party or scratch figures usually isn't a problem, especially if you make good looking ones where it is easy to tell what they are supposed to be. I think converting and scratchbuilding is a major part of the hobby and encourage it personally.

As for what the models are armed with, What You See Is What You Get is the accepted baseline. Models should be using what they are modeled with. This is the official tournament rule. Again, in casual play or even independent tournaments it is normally fine to "proxy" in models as if they had different weapons so long as the opponent agrees to it. This aspect all revolves around courtesy- if you are making reasonably proxies and especially if you are marking them in some way (a sticky note or something even following the squad around), then it is reasonable for an opponent to agree. If you try to proxy every model in your army as using some different wargear than what it has, it becomes frustrating for an opponent to keep track. Just, try and keep things within reason and you'll find that most people are reasonable in return.

If you want a good start and you haven't painted before, going on ebay for a used infantry box wouldn't be the worst idea. Get some used condition models for cheap, strip them if needed, and paint them. An army always has a use for at least a squad of infantry, and you can make your painting mistakes on those before committing to more miniatures.

In fact, if you have an independent store with a good community you should check if it has any open night or Kill Team nights. Kill Team is a good entry point for something in the process of putting together their first few models, and you will likely meet somebody willing to play a starter game with you. From there, you can keep building minis and transition to the full game if it seems like a good fit.

A final factor when it comes to the hobby is the cost of hobby supplies. Don't go crazy right off the bat and buy a million shades of paint because a tutorial told you to. Slow down, get a few foundational colors and a few main colors you'll be using and learn. I reccomend looking at what is offered by a variety of companies not just GW. AK, Vallejo, Army Painter (not my choice), Tamiya, and other brands all have products and it is acceptable to pick and chose. I make my own washes out of artists ink, which is more long term cost effective, if you decide to stick with the hobby. Even the bottom of the barrel Applebarrel or Folk Art craft paints have a role, especially if you are trying to reduce cost. Get some good brush conditioner to help keep your brushes in good shape.

An important thing to bear in mind, especially if you haven't much experience painting miniatures, is that these two armies are amongst the more detailed and therefore more difficult to paint.

With that said, I started with orks and went full in and it has been very rewarding. Admech were my next choice but ultimately went Aeldari instead.

Just 3d print the figures

I don’t know AM, I do know Orks. So Warhammer has something called WYSIWYG (pronounced wissywig) for tournament play it stands for what you see is what you get, essentially those options aren’t fluff they are modeled weapons. It adds some strategy if you are planning to charge with your orks for example as you’re removing models it’s beneficial to get rid of the shooty orks.

I don’t think I’d recommend starting with a combat patrol I find them intimidating and easy to get overwhelmed. Plus you need to see if you like assembly and painting models. For orks just buy a box of boys or nobs(bigger meaner boys) and don’t worry about WYSIWYG as you build do what looks cool to you. Most people as you are learning won’t expect you to have wysiwyg and will instead be kind. If you do a combat patrol I recommend following the guide exactly as the rules for combat patrol do care about loadouts.

The other option is getting an ork vehicle you think is cool. Most vehicles have a role in the game.

There are free rule sets available on wahapedia and new recruit to see the rules that aren’t available in combat patrol.

If it matters to you at all, GW gives a lot more love to Orks than AdMech and so you will not feel as ignored going that route. Both are cool and I got a few AdMech through imperium but they definitely feel like they are going to be a huge challenge for my dumb hands to paint

What interests you about the hobby? Is it playing the tabletop game? Is it the tactical aspect of the aesthetic? Is it building the models? Is it painting the models?

I thought I wanted to get into playing the tabletop game, got some Boyz, and had a blast assembling and modifying them. I love the unique character of each model and the freedom to customize (while having kludges be in-universe and aesthetically accurate).

I've spent more (enjoyable) time building than playing.

My 2 cents: don't buy an army off the bat. Either buy a kit of Boyz (or AdMech) and see if you like it, or, if you just want to play the game, find someone with an extra army, or print out some tokens and play some Poorhammer.

Generally in games there is a rule called WYSIWYG, unless players agree on something different ahead. It’s short for “what you see is what you get”. So if you want your boyz to have stikk bombz you should equip some models with them. They cost some points but you can use them in battle. Once those guys die your squad won’t have the ability to throw them. Usually with smaller details like grenades players would agree to make an exception if you don’t have the models for it. Bigger weapons like rocket launchers, gun choice, close combat weapons, etc should definitely show on the model tho. It’s too confusing to keep track otherwise. Also, idk how strict it is in tournaments, but it’s probably strictly WYSIWYG…

Also, I haven’t played in the new edition yet, so take anything I say with a grain of salt.

My recommendation would be to watch some games with factions you’re interested in, to learn some basic mechanics, before you decide on configurations. There are plenty on YouTube.

I would start by going to the Warhammer community website and downloading the free core rules book and the index cards for the fractions you're interested in. These will explain how to play, and what the rules are for your factions. Learning the rules will be the easiest way to understand how different wargear choices work and which you should choose. You can also go to an official games workshop store if you have one nearby and they will give you a free mini to get you started if you're really just itching to start building and painting. They also make starter paint sets which are a good starting point.