Seriously, the last two years are littered with the corpses of Bitcoin exchanges, wallets and trading platforms. Why would anyone send Bitcoin to a new site at this point?

Wouldn't the first priority be to establish escrow with a trusted third party, or use m-of-n transactions?

At the very least, build the site with full transparency so you can prove publicly, every 24 hours, that you control the private keys to all Bitcoins entrusted to you.