One of the pop-up tutorials during loading screens says to save your starting armor because you can upgrade it to better armor later on. Whether or not that's in the game at the momment, I dunno. And if you sold your starting armor --don't worry. You automatically start with a crafting recipe for it.
Easy rule -
1 - you should, but don't have to save your starting armor. Used as recipe to upgrade to warrior leather armor, your first witcher armor
2 - the armor above can then be sold/dismantled after you out grow it because it upgrades to nothing
3 - can sell/dismantle your first set of witcher swords you find diagrams for (serpent steel and silver swords) since they too upgrade to nothing
4- after that, all witcher gear you find should be saved because they all upgrade to better versions (the light, med, and heavy witcher sets for armor and swords)
---------- Updated at 05:35 PM ----------
Are all doors titled as "closed" openable with proper key, npc etc. etc?
Take this with grain of salt as I've only played twice though Act 1, no further. But so far, the rule that has been 100% true is that if the door just says locked, you'll never open it. It's just one giant **** tease.
But if the door says locked - key required, then you can always open it if you find the hidden / quest provided / found on some body-thing-chest key