.So - until then, I was thinking of taking up gardening on a serious level. My questions are:
Is gardening a good way to make a profit and fund gear?
Gardening can be a decent way to make profit, even at low initial cost (investment) and low risk.
I don't recommend to start gardening on your main though. Most important reasons to avoid gardening on your main are first of all the fact that you have to check your plants regularly (say at least once a day) and you have to be in your mog house to do so and secondly gardening takes up quite a chunk of mog house place, which on a main character with several jobs might be a problem. (Reserve about 20 spots on a char for gardening: 10 pots, some furniture to get Moghancement:Gardening, a few stacks of crystals you intend to use for feeding, room for the seeds you intend to use and room for the crops you'll harvest).
Initial investment is small: 10 pots (some of which you can craft yourself, others can be bought from local vendors for about 1-2K), some furniture and some seeds (farm them or buy them from vendors or AH, whichever is more cost effective).
Focus your gardening efforts on what you intend to use the crops for and what you would like to specialize in:
a) Wildgrass seeds for riskfree, moderate profit (selling to NPC). If you feel up to it, don't NPC/drop the Gysahl Greens you're most likely to grow too. Spend them on chocobo digging instead
b) Cuttings/Saplings for longer term, higher risk but higher profit aimed at AH sales (elemental ores).
c) Various seeds (fruit, vegetable, grain, ...) to grow things you can use to support your crafters (like Wild Onions or Persikos for cooking, various precious metal nuggets for Goldsmithing/Smithing, ...)
d) Cactus stems for risky but profitable yields aimed at AH sales (precious metal ores)
Write down the details of what you do (did), so you can optimize your gardening methods for more profit, based on your own experience. Experiment, and see what works best for you. Try to specialize in one or a few recipes, don't jump from one recipe to another randomly.
Plan ahead for each plant cycle. Make sure you are 100% sure you can inspect your plants at least once a day (especially for the longer grow period of for instance cuttings/saplings, make sure you don't have a business trip or a few days of vacation in between as this would probably let your crop wither and go lost). Try to check plants on the optimum day. Try to plant seeds so that they will deliver crops on the optimum day/moon phase.
Don't be disappointed if your first crop(s) yield useless junk (Little Worms, Rock Salt or Shell Bugs anyone?) Keep trying to find the right recipe and method, but most of all... try to find out if you like Gardening (or at least don't hate it too much).
That's about all the tips I can give you. Good luck!