As a long-time player of this game, the main thing I'll say about gil is... it's not really there.

The big over-arching design behind gil is that a million tiny streams trickle down into your reservoir over time, and you don't really need it for anything important. Really, it's a currency that allows you to be lazy, as everything that can be bought, can be made yourself. And you shouldn't worry about using the market board either, because the game hands you a lot of stuff that you won't need, which you can sell on the marketboard as well.

The biggest reason to need gil would be if you wanted to raid and wanted to be on the "day one" scene, but you didn't want to level your crafters. But if you do put in the effort to level your crafters, you'll find that your gil will just pile up and up, and you won't really find anything to spend it on. I put maybe 2-3 hours a week into crafting what I need for raid, and that's while watching netflix, and I don't really make anything to sell. I'm sitting on a bit of a pile, and that number only goes up, until I find some mount I don't want to go through something like palace of the dead to get, I'll drop 10 mil on that. My biggest purchases are usually 2-3 mil worth of fancy dyes, excepting the time I spent a bunch on housing (bought a dude's house next to my FC, furnished it).

Levelling your crafters need not be expensive either. I was able to get all my crafters up to 50 on a budget of about 2 million gil, which I got naturally through the MSQ (this was heavensward at the time) while selling all my gear I didn't need on the marketboard. You can buy mats off the npc merchants to grind up the crafters, or if you wanted to go even more long term, you can do exclusively leves and grand company turn-ins to get to 50 slower, but turn a pure profit. If I were to do it all over again on a new character (I won't), I would plan to level the gatherers at the same time so I wouldn't have to pay for any mats, and would turn a profit just levelling. Doing it this way also means you can craft all your new gear as you level.

Once you learn all the little places it trickles in and where to get the things you need instead of spending on it, your wealth will grow naturally.