Hi Br-Real,
Thank you for your question.
Yes, you can use other assets like open.btc or BitUSD as collateral with MPA too. That is more or less the second stage progress when enough BitUSD have been created. BTS is not inflating right now, there is a limit amount of BTS in existence that will not change.
For the creation of BitBRL, you need to buy BTS first, then issue the MPA and sell it for a small premium to the market. The BTS price is very low and stable right now so it can make sense. But also consider increasing your collateral if needed.
MPA market fee is 0% right now. In case we really need to change it then the committee members can initiate a change.
Thanks !