yeah best to keep it seperate, cross-collateralising is never a good idea for the aboved mentioned reason. Its a common strategy of banks, Bankwest is one example. It increases your risk, if you have to sell your investment for whatever reason you will not be able to because you have the two loans as collateralised as one.
A great book i’ve just read called “From 0 to 130 Properties in 3.5 years” recommends Steve McKnght and Dave Bradley. Don’t ask me if there any good at accounting though, but i know there good at investing :P