As mentioned earlier in the thread, you don't need your alts to be level 50 themselves to do max-tier writs; the writs' level is determined by the character's skill in that particular craft. I have a few level ~30 characters that have their craft skills leveled up to 50, and they do the same exact writs as my master crafters. So don't go out of your way leveling alts for that reason alone, tis unnecessary.

As for leveling the crafts themselves? Provisioning, Enchanting, and Alchemy can all be done more or less "instantly", given you have the materials. The short version is "craft enough food/drink til you're level 50", "create enough poisons and learn alchemy ingredients' traits until you hit 50", and "gather a LOT of glyphs and deconstruct them until you hit 50". There's a bit more to it than that if you want to do it efficiently (and you should, because it's costly no matter how you slice it), but that's the gist. All three of those crafts combined can be done in like half an hour (if you have the materials). Alcast has a handy guide here. (just navigate to alchemy & enchanting via the menu at the top; that link's for provisioning)

The "hard" crafts -- blacksmithing, clothing, woodworking, & jewelry (if you have access) -- all work pretty similarly; most people just decon items on the long road to level 50 (again, talking about the crafting skill 50, not character level here). It takes a LOT of stuff to level up that far, but that's how it's done as far as I know. It takes longer, just because of the amount of fodder needed. Most people don't have thousands of trash items just lying in wait. You also get small amounts of xp for creating items and doing writs (even the lower level ones), but this would take longer, and cost a lot in materials.

If I'm not mistaken, all writ levels have the same gold payout, though. You don't need to do them at max level for good payout (unless I'm mistaken). It's just more convenient, as all your characters are using the same materials; cuts down on farming a slew of various raw materials. Doing all 7 writs nets me 4,648 gold per character per day. Multiply that by however many characters you care to do the writs on, and that's your base pay. You'll get valuable items you can sell for more, as well. I get just under 80K gold each day this way; not even counting the bonus items.

All that said? Writs are something of a tedious chore, and while it's worth it (subjectively, at least), it's certainly not for everyone. Doing this on your limited free time might make you hate the game entirely for all I know. You gotta find something that's actually enjoyable (or at the very least tolerable) for you. It's your free time, and none of us can tell you what will be best for you personally.

But at least you know the basics now! : P

More fun ways of earning gold? Echoing and adding to what other's have said above:
- Running dungeons and trials for motifs! Always in demand, and have a good sell value vs effort to acquire.
- Farming for sellable gear pieces! Depending on how much you enjoy the various methods of seeking said items.
- Harvesting raw materials for others to buy! Lots of crafters & writ doers don't wanna harvest their own mats, so selling them is an evergreen market; it's also extremely low-stress and accessible, if you're not into "hard" content.
- PvP! If you're into it, you can turn your Alliance Points ("AP") & Tel Var into gold in a lot of ways. There's always PvEers looking to buy things without needing to set foot in PvP content. Always.
- Buying & Selling! Some folks play the ESO economy like a market, and just go around buying up under-priced goods on guild traders, and selling at-value (or above, depending on their trader location and other factors) -- and these people can make millions per day. There are good guides floating around out there, but it's about as straightforward as it sounds afaik. Easier on PC with addons.

Good luck!
: )

Sorry for the wall of text, haha