A grinder upgrade sounds like it would be worthwhile, but I think you can get by with the virtuoso for now, the preciso might be a good if you can get a deal, and I like the PL53 too, no experience with the Rocky though. And getting a blend that's forgiving of dose will also give you more room to play around, you won't have to nail the grind right on if you can dose a little more or less to get the shot to flow (and taste) right.
The bottomless portafilter will definitely let you know how much work you need to do to distribute the grounds. My favorite ways of breaking up clumps and distributing are either the WDT (vigorously working a thin needles through the grinds, good for really clumpy grinders) or a simple nutating tamp (for grinds that just need a little help).
You can put in a lot of work trying to manage the temp and still not be very consistent, so a big part of it is getting coffee that doesn't mind temp swings, and feeling lucky also helps

But you should be able to get an idea if you're in the ballpark by just tasting the shot, ie. it shouldn't be too hot to drink, but it should still be hot (make sure you preheat the cups with some hot water or something). And a styrofoam cup and cheap thermometer will give you a good guess too - basically just make sure your machine isn't broken (it's probably fine).
It sounds like you're on the right track though, I think you just need some good coffee + practice (but I think that's true for all of us).