Leveling crafting whilst leveling DoW/DoM classes

[Kydi]

Are there particular gathering/crafting skills that would complement armourer? Unfortunately I only get a couple of hours an evening to do anything, if that, so would rather try to avoid having to level 4 additional skills. Obviously mining for ore, but would leatherwork or carpenter be better? I'm leaning towards leatherwork since if I can get skins by just playing and craft the hides from that it would be preferable to gathering, crafting, then using those crafts to craft more.

[Niwashi]

How can I level crafts without making myself bankrupt, or do I need to level gathering and other crafts too so I can supply myself with materials?

I think you answered your own question there. You can either do it the expensive way or the time-consuming way. Most people who really get into crafting opt for the time consuming way of leveling all (or most) of the crafting/gathering classes together.

Other shortcuts that can help include knowing what materials you can get from NPCs (some things can be bought from very specific locations - and only specific locations!)

The Libra Eorzea app is good for checking these.

using crafting levequests to maximize your experience-per-craft (and get some rewards back), etc.

And the supply/provision missions from your GC. They're limited to once a day, but they give a huge XP boost (as well as GC seals). Even up into the upper 20's and low 30's, I can still gain a level every couple turn-ins or so just from supply missions alone.

Are there particular gathering/crafting skills that would complement armourer?

Leatherworker would be good for supporting armourer, but then you'll find leatherworker itself needs support from weaver, etc. All six of the main gear-focused crafting classes end up being co-dependent on each other for materials. Culinarian and alchemist stand apart as somewhat less necessary in that regard. (You may still need an occasional item from ALC, but not often.) But they provide good cross-class skills useful to other crafting classes. (At level 15, those are Hasty Touch from CUL and Tricks of the Trade from ALC, both of which help at dealing with a shortage of Crafting Points common while leveling up any crafting class.)