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. 😁

I have probably 60 or so mods on mine.

My $.02.