Yes
You can but you will probably need a 10.000 to 20.000 EUR bank to make it worthwhile. My ROI is above 2% on Tennis, Basketball, Hockey and Am. football with the sharps and above 4% with one bookie (more than 7000 bets in total). Football is only at 0.5% as you mention.
Have a look around and see how much money the sharps will let you wager. I think that is the main problem. But SBO is not great. They will lower the offered odds to you when you start winning.
Same here. 3et never responded to my enquiry about an account. But the 3et feed on rebel shares 90% of its odds with IBC and ISN (sportmarket for example) so you can just use that.