I'd say go with whatever you have a taste for, really. But if you want recommendations, for something different, I guessed I'd suggest a washed curd cheese, like a Gouda. Though you might also want to go with something that is quicker to age, just so you get a chance to taste. Colby is a washed curd cheese that only ages for one month. Caerphilly is kind of a cheddar light that ages for three weeks. For slightly more interesting makes you could go for a drunken goat/drunken cow, also for a month. But really, go for whatever you have a taste for.
As far as pH tester, I'd say for now that you probably don't need it (unless you want a new cheesemaking gadget). It will help you figure out what exactly is going on and hew closer to standardizing your recipes, but for the moment I'd just experiment with the recipes. Unless something turns out very wrong with your cheeses you should be fine without. I'm saying this as someone who's made a little over a dozen cheeses and doesn't have a pH tester. (Although, none of the recipes I've run into have full pH information, so I've not really been tempted to do more than get some pH strips to check and see how acidic the brine of my feta is)