If you read back through this thread you can see that a few of us are happily using Pinballia cabs. I'm on a HD 3 screen 32" and am happy with it, a couple of others are running full sized 4k. The cabs work well but to get the most out of them it helps to get familiar with the software to be able to update it, and update the tables to the latest versions. I also ask them to upgrade your hardrive to at least 1 TB. Pinballia tend to clutter their cabs with a load of older tables but you should think of it as you're not paying for the software, you're paying for the cab. The software is all community free software. In terms of the cab specs you can look to update the PC if you're more confident than me with that sort of thing like ballsports, or just have the table set up as it comes and you'll be happy.
I'm not really a video gamer, so I'm happy with my 60HRZ HD machine. I'd prefer 120HRZ over 4K but I also don't have any lag with mine so it seems smooth enough to me. There are literally 1000s of tables available but I've got just over 200 on my machine at the moment all playing very well and I'd say my wife and I only really play around 30 of them regularly. Higher quality with less table options is what's important.