FC build would be possible somewhere between job 14~23 (ideally starting at 23, since that allows max FC+TC) - note: it will be harsh SP-wise to do solo FC early on as you won't have RD10 and PA yet (which would be job 47); the damage won't be good at first (especially at job 14, with only lvl 1 TC) though it will scale up steadily with your base level;
ATK (include card/gear %damage mods) and mHP are the main factors (mSP is rather insignificant) - so have as much gear that provides such on your setup (among the gears you already have, prioritize using those);
wild cat d.robe is more like a gfisting armor (back before newer cards/gears) rather than an FC armor - should work on getting glorious suit (TI/OPB > EMB > KvM badges)
mHP gears contribute to FC/TC damage (so might as well treat those as "damage" gears too) - they also improve survivability, so they are cost effective indeed;
as for nid-garb, it won't be useful at higher levels - but you can make use of it early on until you have enough to get a VIT-GFSS (this would be the usual high-end garment for FC damage, but costs a lot - for the meantime, you may actually want to just keep the nid for use);
HBP would be an alternative garment, ideally at +9 with 90 STR and VIT;
VIT-GFSS will still be the best (combined with temporal STR/VIT boots) - though getting these usually means aiming to achieve clean 1- or 2-shots on specific mobs / leveling areas, as otherwise, the cost may not be worth that much (unless you simply have funds to spare and want to maximize damage)
if not using GFSS, variants (cheap) or +9 superior e-variants (not cheap) would be the best for shoes;
2x medal of honor (aco) for accesories;
just focus on getting levels for now and not worry to much about maximizing damage (even if you don't 1-shot, you can just repeat FCing anyways);
for weapon, 2x racial cargas for damage;
racial thanatos mace (costs more) are nice in that it has HP/SP regain chance, 180 ATK lvl 4 weapon, and has VIT+6 (more HP for more FC/TC damage);
since you have WPH already, if you combo with alarm mask and pumpkins, you may not need HP regain gears (RWH, HF cards) that much, though if your damage is more than enough those can be handy;
best to focus on mHP gears for now; ATK would be better if your setup has high %damage stacked;