Entrepreneur

So a friend of mine told me about an idea for a startup. Without going into to much detail, a large part of the work would be processing payments, received by various people in various currencies and then pooled and later (at fixed times) paid out to recipients, again in various currencies depending on the recipients.

So let's say you may have 10 people paying in a total of $100, £50 and €60, this is then collected and has to paid out with a 50/50 split to 2 recipients, one of which takes either Dollars or Euros but not Pounds, and the other one only takes Bitcoins.

My suggestion was to have an internal unit of account, so when you receive the money in the different currencies you immediately write down their value in that unit of account when the money comes in, and when the money comes you convert it the same way to the payout currencies. There's some risk of exchange rates changing in between but that's a separate issue.

The thing is - what is a sensible unit of account to use? 1. just pick one currency, e.g. USD, and use that? 2. make a currency basket, either your own one or use an established one like XDR (special drawing rights) although XDR also includes CNY which is irrelevant in this case)? 3. convert everything to gold (again, just for accounting purposes) as a neutral store of value? (dont know if there's a problem with arbitrage with more exotic pairs such as Bitcoin to Gold) (also I guess the Gold value tends to go up as more money is printed than gold mined, so you might "lose" on the FX during pay in and later pay out? idk)

Just wondering if anyone has a suggestion or could point me towards any resources.