Can I buy multiple humble bundles?

Yes you can. I did that too.

You can buy multiple ones. Two for sure, without seeming shady or anything. Back in the Jumbo bundle time i've bought it twice, because I didn't know I can raise the first one's 1$ to the BTA :)

Yes, it will look like:
Click

Alright one more question, they won't do anything if I get 3 right?

A friend of mine tells me that you can only purchase 4 or 5 max per day. Then Humble Bundle won't allow you to buy anymore. This is what the Humble Support tells him when he submitted a support ticket.