1. What percentage of liquidity are we still getting from Stamp on average?
I do not see Bitfinex integrated with Bitstamp anymore. I think all the liquidity is at Bitfinex only.
Not correct. We are still integrated with Stamp (read the last release notes). The orders are all just blended on the screen and labelled as BFX, but many still are from Stamp.
For the remaining concerns, the simplest solution is to simply hire someone like Andreas Antonopoulos to come validate your BTC balances, fiat balances (ie witness you login to your bank), Stamp balances
That is a typical financial audit, which any accounting firm can do. The key is to get a world wide recognized firm, not a local CPA with no name recognition. Too much potential for abuse (buying the opinion) with a no-name firm. This also needs to be done on a regular basis (at least quarterly, preferably monthly).
I agree that only a well known (big four) audit firm should be used, but in the interim Andreas can give us a good level of confidence on almost all the points I mentioned in a very short time, for low cost. Again - follow Coinbase's lead until a more robust solution is accepted industry wide. It's important to put fear to rest and get on with business.