If I want to create my own currency model what would be the best basic options / things / ideas I need to look into?
In fractional reserve banking the money supply goes up and down according to the rate of new money being created as new loans are made and the rate at which existing money is destroyed as loan (principal) is repaid. So your model needs to include some estimate of the mutual enthusiasm, between banks and their customers, for making new loans. This in turn will be a function of the interest rate amongst other things (IMHO most importantly, people's perception of the future trajectory of house prices).

BTW, I hope you're not assuming that the money supply is capped according to the money multiplier story. That's all completely wrong as the Bank of England confirm => here.

An alternative is full reserve banking where the money supply does not go up and down with loans/repayments. In this case new money can only be created by the government/central bank. This would be far easier to model. When looking at full reserve banking - don't be misled into believing that banks can not lend in such a system (as some textbooks may imply). Peer to peer lenders (e.g. zopa) are essentially full reserve banks and they exist already.