The custom items are fine.
Sorry I haven't put more together on the Borogashi already. Feel free to make it up yourself.
If you have time feel free to do write ups of her class features. It would be helpful but by no means required. Just page numbers would be fine.
Yes same number of slots, same affinities too. Borogashi may sport dorsal and caudal (tail fin) rings rather than a cloak and boots. A dorsal ring can accept the enchantments any item in the shoulder slot could.
490k would still be the absolute maximum you could borrow at game start. Going above the standard wealth allotment involves karmic debt rather than financial. So even if you made enough money to pay back the balance very quickly, poor luck and hidden enemies would continue to plague you at least until the end of the first storyline. Considering the usual pace of PbP play and that there isn't a set end for the story, that could be a while. Going over the allotment by 10% would result in only minor complications, more than and it 15% starts to get nasty. At 30% over the betrayals and bad breaks would be constant, and by 50% your character's whole focus would be about staying that one step ahead of a fate worse than death.