Customized ICO contract

Hi guys,
I’m new on POA. First of all I want to say that’s a great app.

I want to create an ICO smart contract with a few particular things which it seems that I can’t figure out how to change them.

First of all. I want to have 3 tiers. in the first tier a presale with a fix token number, second tier the ico, and third and after ico tier with 25% bonus.

Ofcourse we have to keep 10%, and the team should get 5% from total tokens but…

I would like the tokens to be issued as they are purchased during the presale and during the ico. My question is, would the contract adjust automatically the 15% to the total amount of tokens?

And my second question is if we in the 3rd tier we would offer a 25% bonus (after the ICO) where you mention in the contract wizard how many tokens per ether the rate, and the total number of supplied tokens… do I have to pre-calculate the 25%, for example if we offer 100 + 25% I’ll put 125 in that field and also the quantity of the total supply should include those 25%?

I would like to raise as much as possible so not having a fix number of tokens I think might be a good option, if we raise $100.000 or $1.000.000 without having to refund in case we don’t reach our goal, and without a specific target, can you please explain me how can I do this?

Thank you very much!