There are many charges with betfair and you have to understand them all to understand if you will need to pay more. Basically :

1. Turnover charges may apply if your backing
2. Premium charges will apply if your winning consistently
3. Data Charges will apply if you make too many calls per second (20 calls).
4. Commission is charged on all winning bets
5. Inactive Charges - If you set up an account then don't use it
6. Deposit/Withdrawal charges depending on how you do it.
7. Higher Premium Charges (different to premium charges) for those who are really good at profiting.

Overall If you have a bot you should be able to code it to do more then 1 system. Mine runs heaps and uses the same data to apply to all systems and makes bets on that.

You can get your account banned for the following:
1. Betting under minimum stakes
2. Not betting but running a bot( regarded as price collection which is against their terms and conditions)
3. Money Laundering
4. Trying to avoid premium charges.

Overall its easy enough as long as your not trying to game the system and you abide by their rules.