I think chain from the start yea. Yea I made a bunch as a blacksmith but also found corroded on deadites. The tradeskills were alot more simple back then but I think now you can polish up corroded stuff into tarnished maybe.
Corroded into tarnished is still in game and super easy, as long as you get the armor to drop, it's all you really need (scrap extra into parts, then combine with a piece to make tarnished).
It may be the case that drops themselves are isolated to various mob groups, where some mob areas will only drop cloth/leather and others only drop chain/plate? For example, I've only seen the level 1 - 10 gnoll like mobs (ashari or whatever) drop cloth/leather. I've never seen a piece of plate/chain drop, but my characters are all level 12 or lower, so maybe it's a level thing instead.
As for making it yourself, it doesn't take tooooo long to craft up some copper. If the noob areas are busy, you can pick an area with 3 or 4 nodes and just camp them for ore. It seems faster than running around willy nilly. Then you need to farm up leather scraps (or buy them) and make them into straps. Easiest to make an alt and start them with leatherworking at 25. Everything after copper required higher level leather straps and those will be the hold up on crafting your own armor.