Install SSD, 3 answer

Hi all, thank you first for reading and maybe replying my answer (wtf my english, sorry).

I know i could search on the web, but on it i couldn't find all I needed. I'm here because I need to replace my HDD with an SSD. I didn't understand 3 thing:

1) I have a SATA 2 on my iMac and the SSD is SATA 3. Ofc I'll lose performance, so... Can I do something to resolve that? (Change my iMac SATA maybe?)

2) My iMac will not be filled up, so I can put my SSD as first and only HD. Is that ok? Can I do that? (Or it's better to put it together my default HHD [it's called fusion drive right?])

3) I read that to put my SSD I need at all cost to remove my SuperDrive (CD and DVD drive) and then but a support, is that right?

I know, a lot of answer, but I say thank you a lot if u can reply completely.

Ty for your time and patience again.

BB - Alberto