I'm also a Probemaster user (extensively actually). And although I have stuff from both the 8000 series and 9000 series, I'd recommend the latter if you want to use more than the typical probe tips. The reason being, the 9000 series is modular, so they don't attach to the probe; just the lead wire. Which means you don't have the probe weight hanging off of your test point, so your attachment is far more likely to stay put instead of slipping off. BTDT, so I've become fond of attachments that attach directly to the lead rather than the probe. YMMV, depending on what you're working on however.
If all you need are a basic set of probes, the 8000 series are excellent.
FWIW, they only offer spring loaded probes using the 8000 series probe body, and they're excellent; much better than the Fluke/Pomona equivalents.
Regardless of the series you choose, the kits are less expensive than buying individually. Equivalently speaking, they're also less expensive than Fluke/Pomona, yet don't sacrifice quality in doing so.
As per meter connector ends, the retractable types are effectively universal IME, yet offer some additional protection during insertion/removal; meaning they'll fit old equipment (pre-shrouded input jacks), as well as more recent stuff that uses shrouded input jacks. That said, you can still knock yourself on your ass if you're not paying attention, no matter the lead version.