Your ph is fine, but it is a good idea to be sure the surface of the water is moving because it keeps the lower parts fresh with oxygen for them to breathe. You will see it change for diff times of day and how much fresh air is in the room too (like if a window is open).
If you didn't buy the skimmer yet, I wouldn't feel rushed to do it. Your tank can handle a couple fish just fine and with skimmers you seem to really get what you pay for, so if it's a question of $ I think it's smarter to save up for a good one and take your time to read up on the reviews or wait for a sale. Imo a 20g doesn't need one, but if you want it best to buy carefully.
It sounds like your cycle is off to a good start, but I'd hold off on the clown fish a little longer. Your tank doesn't have any snails or anything, right? are you adding a little food or something to get the ammonia going?