i would highly suggest diamond gear to boost your main dmg spell FoL 2 (based on para res) but that equip is gone on official which means it might be gone here someday as well... so 2nd best would be the BG gears since fuwa modo is a tank and has a few HP based dmg spells
as for your build, it can vary alot based on your playstyle... playing as modo means you have to focus on different forms, personally for pve i play demon main and human as secondary, but for pvp i have more luck playing demon main with modon form as secondary, but if you play around with it, you'll find what works best for your playstyle

this is my pvp build for fuwa modo with modon backup:
http://jd.pwdatabase.com/pwi/calc/Modo#r27z1z53951z36031z8803609c0a3a3609c698a625403m4222412222333322222223223322323333&81key notes on using this build: its best for modo pre fuwa modo and focuses on fasting and bleeds in modon form and enhancing the stun of SA and SA2, the dmg of FoL2, and sp burns while in demon form
i typically start a duel in modon form and buff up with firestone will and nimble, then try to fast them with spiritual charm, then switch to demon form and buff up my res with ghoulish night and then secluded sprig and immediatly pound them with FOL 2, then i try to fast them again with the modo asc skill if they are not fasted yet, if they are, i switch to stun mode and go modon for a moment to rebuff if needed and hit them with snake bind to lower their res, then back to demon to stun them with Surprise assault and/or silence them with Surprise assault 2...
this is just a base run, it varies alot so once you've pvp'd against a specific class a couple times you'll change up your strat for that class

for sp burns you have the modo asc skill that wipes 60% instantly and i use scepter bleed and sin orb bleeds to really boost that sp burn, then use the modo asc buff that resets the 60% sp burn skill and hit them with it again to fully wipe their sp (works great if you get a fast to stick either from modo asc skill or spiritual charm in modon form)