Getting a Unit this week.

I am starting witha Surly 20 or 21 tooth sprocket as i need to slowly get fit.

I am concerned the larger sprocket will need a longer chain. Anybody know if there will be a problem here or just a matter of adjusting sliders?

Also, what if I want to replace chain with a Sram. i have been told 8 speed Sram will work but I imagine will have to drop a whole lot of links.