Several walkthrus talk about storing and selling weapons but weapons won't go in the inventory (bag) so how do you pick up and store the dozens of weapons you come across in game?

You sure those were for Witcher 1 and not Witcher 3? As far as I recall, you couldn't have multiple swords in Witcher 1.

You know what: Scratch that. It's been so long, I'm not sure.

There is a mod that gives you access to your storage whereever you are so you can pick up extra swords and daggers and place them in your stash, then retrieve them later to sell.

IIRC, you can't have additional swords in your satchel/bag in The Witcher 1, so a sword will go directly from storage to your steel/silver sword slot, replacing your currently chosen weapon. So, in order to sell a sword, you need to equip it, visit the trader, get your orens, become temporarily unarmed, and go back to the inn to get your previous sword back from storage (or to wherever you dropped the sword, it should still be there).

No, dropped items disappear when you leave the area.

You're right, it's only certain quest items that stay on the floor.

Fortunately I didn't find necessary to change swords too often in The Witcher 1.

That's one thing I hated about the first Witcher game. There's hardly any point in picking up other weapons than the ones you've already equipped, but you still find the same old junk loot behind every corner. Make up your mind - what good is a load of loot, if you have no use for it? Either do away with the abundance of loot or make the loot more interesting and useful. It seems as if they just adopted the loot mechanics from NWN without really adapting it to their game.

Keep your waist "additional weapon" slot free. If you see a weapon/sword that you want to sell later you can use this slot to lump it back to town. But unless you want a collection in your inventory or are trying to grind for coin it's not usually worth it. It's actually easier to ignore dropped weapons and grind on drowners / bleeders etc for alchemical ingredients to sell.

Biggest mistake I made was losing my Silver Sword when picking up weapons. Went the majority of the game without it

Getting money by selling weapons in Witcher 1 requires a crazy amount of dedication, as the inventory system isn't meant for hauling a lot of stuff. Really, if you'd mod out the dropped enemy weapons, the game wouldn't suffer one bit of it.

You can equip a second sword on your hip instead of an axe or dagger. You can put a dagger in your ankle slot.