MeseCraft is a good starting point that provides a much better not-just-minecraft-clone experience than the base game. From there, i3 provides a better inventory, and I haven't really screwed with much else.
Depends what you want to do. Mesecons and digilines will give you redstone type stuff, and a lot more. Animalia is good. Farming mods, aquaculture, maybe a mobs pack. Cave realms is good but only if you plan on digging deep.
One thing to keep in mind is minetest is entirely about the mods. So you can customize the game how you like. It also means the base game provides very little. 😁
Honestly, I've stuck around for NodeCore. It's not like Minecraft at all, it's something totally new. It's very minimalist at the moment but you might find that makes it easier to pick up.