The SR20 prop clearance is 8" for the 3 blade (which we have) and 7" for the 2 blade. I’ve never found prop clearance to be an issue, I certainly would be worried about operating from a strip where the grass was long enough to touch the prop! The position of the nosewheel tends to ensure that the prop stays above the ground - I’ve taxied through depressions and drainage channels without problems, but the advice to walk the ground first is very sound.
As far as types of surface go, I’ve been in (and out!) of various dirt, gravel and grass strips. A good gravel strip is nearly as good as a sealed surface, but watch out for stone chips on the prop - if the surface has loose gravel, it’s best to do the runups while taxiing - i.e. check the prop governor as you start the taxi roll, check the magnetos during ing the taxi.
As far as length goes, I have a rule of thumb that I want a minimum 800m (about 2500’) of runway. The longest ground roll that I’ve measured in any sense was about 400m of short, very wet and soft grass at max gross. So my 800m rule of thumb is conservative, but fortunately here in Oz most unpaved strips are of reasonable length. If the strip was less than 800m I would be carefully checking the approaches for trees and other obstructions, checking density altitude etc. etc. Unpaved strips often have trees or powerlines at the ends.
Getting in is never a problem - I would reckon the SR20 could be landed with 150m ground roll, and it slips well so getting in over trees or powerlines is not a problem, but getting in is no good if you can’t get out!