I'd do Armor, pick and sword, not in any particular order and add bow and fishing pole later.
If you use the bow a lot then it would be more important. And it's quite likely you'd get all the enchanted fishing poles you need from fishing.
Check one of each and see which gives you the best enchantment and if none are particularly good try putting torches in front of some of the bookcases to see if you get something better, don't forget to remove the torches before the next round.
Also when you run below 30 enchanting levels you can add a torch or two to get say a level 28 enchantment to squeeze in one more.
Fortune is very nice for extra diamonds, also it's good for harvesting potatoes or so, and that doesn't even wear it down.
And Infinity on a Bow, unless you have a skellie or chicken farm for arrows.
If you've got the diamonds then go for it (don't forget to get Fortune as soon as possible), the items, and therefore enchantments, will last much longer.
Don't forget that fishing can be a good source for enchanted books, or Villager trading, though I've never liked that myself.
In the beginning when you don't have an excess of diamonds use iron if all the available enchantments are just so so.
If none of them are any good you can enchant a stone tool or something just to change the enchantments.