Simple guide since I've decided to spend my time recently increasing my space for Salvage, and since there's multiple ways I wanted to start laying them all out for anyone else that is trying to max out the space they can have, to make more AD.
Each character starts with a 6x5 bag Adventurer's Satchel and you can claim 6x3 bag Adventurer's Knapsack from "Close to the Crown" quest found in Blacklake District, and is very easy to get to for your alts. As for the 6x2 bag Adventurer's Pack from the quest "Clockwork Guild Tomb" in Neverdeath Graveyard, personally I wouldn't recommend getting this one on all your alts, simply due to the amount of quest you have to do pre-hand, but it does grant you some space, and is a bit easier than other ones you can claim. They also start with a personal bank 8x2 space. There are more bags you can get on alts, but I wouldn't recommended them simply due to the time it takes to get them. :P
Optional: Dragonborn Legend Pack, contains the 6x5 bag Dragon Hoard that can be claimed on each of your characters, which is huge depending on the amount of Alts you have, but due to the price it's fine if you skip this one.
A not very widely used storage place is companions, get yourself some cheap companions on all your alts and you can store random pieces of salvage on them as long as it's the right type of item of coarse, the ones that cost 5 gold a piece will do just fine.
One that I tend to forget is the mailbox, sending salvage to yourself via the mail works, mind you there is a limit. ^-^
Now there's a lot of things you can purchase with Zen to increase your space, which is why I wouldn't recommended the Dragonborn Legend Pack if ya don't already have a lot of alts. ^.^ Here's what you should think of buying first to increase your salvage space. Nice way to go about making room. Character slots, simply due to the amount of space you'd get from them makes it all the more worth it(up to 50, not counting the ones from packs.) Companions with easy to fill space on ya alts. (recommend)Shared Bank slots, I'd recommend about 4 to 5 rows, it really helps when you farm salvage. Dragonborn Legend Pack, once you have a decent amount of Characters unlocked, grants you up to 1,490 salvage slots if ya have 50 alts. I'd recommend once you've gotten all of the above, if you haven't already purchased the other packs that grant a character slot then grab them as well. At this point you can start buying Bank space, start with your main, since you can get quite a lot of extra space from it, atm I'm at about 22x8 in my bank. c: Runic bag of Holding on alts can work as well, if you so please. If for some reason your still after more space I don't think there's a cap on the purchasing the level 70 characters. ^-^