The only true purpose of any 'base' is to store things, craft, sleep, enchant, and maybe make potions. Anything else is really just decoration. Minecraft players don't sit around in their base, watching TV, shooting the breeze.
That's not to say it's useless... it's great to make a really nice looking base! I'm just talking in practical terms, and functionally.
Beyond that, I generally have almost all types of farm within the 128 blocks of the base, ie the loaded area. Some to prioritize are.
-A reasonable-size manual or semi-auto farm; primarily for wheat; can also be used for potato/carrot/beet. Because you need some wheat to breed cows
-A cow farm. For leather, for books. For enchanting.
-A cane farm, for books.
-A chicken farm, for feathers, for arrows.
You can also get the books from villages or strongholds. And you might also get an infinity bow, and not worry about arrows.
Tree farm. (Might be really simple at first, ie just a place to plant them. I like putting slabs 7 blocks above though, at least, to avoid the hassle of chopping down the huge trees)
Villager breeding. Because next priority is usually an iron farm; I like the simple ones (e.g. Docm77-style), to get maybe a stack per hour or so; enough for a full beacon
AFK fishing, if you're gonna do that. It's very productive.
Enhance the villager breeder so you can keep the good ones to trade with, and kill off the crap ones.
Very fast micro bonemeal wheat/potato/carrot/beet farm, mostly to get massive amounts of carrot/potato to trade with villagers.
General darkroom mob farm, and/or creeper-only darkroom spawning.
Auto-sorted inventory system; optionally with shulkers.
Others (for lulz, really) include a horse farm [breeding the better ones; stables can be cool and fun], all the other animals (esp sheep; coloured wools can be handy for some builds) (and I do like llama too), and possibly 'pretty' farms for all crops, although if you have a skelly spawner for bones, those become mostly decoration.
(I've left out things that are place-dependent, which is usually gold-farm [because it's probably best above the nether; you can make one overworld using portals though], dungeon mob-farms, blaze farm, wither skelly killing zone or farm, etc.)
A 'record' farm is always quite a good, fun challenge.
i guess a lot of it depends on how much you just want to be practical (in getting better gear ASAP), and how much you want it to look nice. But anyway, I hope that gives some ideas.