In Need of Advice

[Mac's RR]

I’m looking at giving my bike some more lower end power (a 2007 CBR 600 RR), so I'm looking at getting a new Rear sprocket. I have a few questions before I purchase this sprocket.
1. What is a good size sprocket? (Mine is a 42T now)
2. Do I need to replace the front at the same time I'm replacing the rear?
3. Should I or do I need to replace the chain as well?

Any advice would be great.

Thanks.

[Grashopr]

replacing the rear sprocket isn't typically the first 'mod' to make in gearing. Typically, riders swap out their front sprocket for a -1 (stock size minus one tooth). Each tooth on the front sprocket is worth approximately 3 teeth on the rear sprocket. So you COULD achieve the same gearing as a -1 front sprocket by going to a +3 rear sprocket, but fronts are cheaper and arguably easier to swap out. If you aren't going to go a full tooth down in the front, possibly go up 2 teeth or even just 1 tooth in the rear for a little extra bottom end away from stop lights. Everything I own has AT LEAST -1 in the front, and my 675 gets ran with a -1 front +1 rear occasionally.

[Mac's RR]

You really think changing the front sprocket is easier?