Im questing around and picking up armour pieces and weapons that are far superior to the ones I can craft at my level.
It's not even worth it to craft weapons and armour. They come with no bonuses, are usually useless compared to what can be found in the world and some treasure hunts seem to be level gated so that when the armour/weapons are useful, they are either blocked away or way too far up the level tiers. Crafting needs another good look.
The balancing between crafting weapons and armour across all levels is so messed up right now.

It usually is early in game or low level in most games.

In "most" games (RPG) you will find only gear fitting your low level. Bones and branches for maces, rusted knives andwhatnot - mostly junk that you will gladly throw away after you have gained one or two levels.

But, W3 does many things differently, for the good or bad.

One example would be the witcher's gear, from armor to weapon. There are treasure hunts for these pieces of equipment, and - even if a full set certainly is not that bad, you will get equally good (often better) gear throughout the game from merchants or simply by doing your (side-)quests.
Would have been nice if wearing a full witcher set of any school had been the most Geralt could acchieve. It is not, sadly.

It's a question of preference, I usually find the bonuses of the witcher gear to be better than other gear (especially the exp bonus from some witcher swords) that I prefer to keep using them, even if it mean slightly lower damage/armor.

What bonuses? Is there a way to see what bonuses I can get if I wear the entire school of armour/weapons?

Yes that is correct but some games if you can run fast enough then you CAN score some good gear and weapons,if you know where to look.Might and Magic series is a good example with a hired locksmith and a gate keeper to instant travel back to safety:-)

... where the white ones are attributes that the item initially has,
the yellow ones are those given by runes (from you, the player),
and the green ones the attributes you get by using witcher gear (same school).
Meaning: the bonuses of the witcher gear are relative to the amount of gear (witcher stuff) you actually have equipped.

So, if you do not count wearing/using witcher stuff as priority, there are items to be found (weapon and armor) that
- have higher attributes
- can be further updated by a certain merchant in HoS.

If you look at the basic stats of gear out of W&B, and then add what is possible if you visit HoS - easy to create a tank (without your magic abilities being fiddled with).