DrPepsidew: I'm quite fond of it since I discovered it works well in right spin, tbh
@Izkhoort: I generally just assemble my spare parts into random combos to play around with, perhaps do that? If you get Burning Kerberous then you can use its SG (with an shielded ball bearing in place of the metal one) in Wolborg 2's Base anyway, though, which is a really good zombie setup perhaps?
ShinobuXD: Yes that's still legal. Plastics gen was always kinda loose with legality in general, especially because takara used generic, widely available parts for the gimmicks of bases such as metal balls and bearings, but that's not even remotely close. Remember this is a generation where you can unscrew metal ball base and have to use a screwdriver to put some tops together. Part of why I like it so much tbh!
As for recommendations you've got most of the staples, good buying! You're missing an HMC so a Metal Driger would be the obvious thing. Driger V2 would be a good choice after that, and you don't have Wide Survivor, so there's that too. Dragoon G would help you try out left spin attack, and Driger G is always a good purchase if you can find one that didn't get touched by the price hike, though you could use Driger V2's AR instead if you get that it's more prone to breakage soooo.
After that, obviously you could try to find a grip base and/or look at more complex attack setups, and a second wide defense would help with testing etc. I personally find a compact using Metal Ball Base makes a great opponent for general testing of things to see if they work well once you're used to how well known stuff works against it, so that could be useful.
Dragoon S or F are good for regular left casings but you can just use neo ones instead so no big hurry - takara dragoon S might let you verify the tests I did a while back and everything I've tried since that shows that upper attack is pretty much useless against even compacts let alone defense, though there's no real need haha.
After most of that you're basically set unless you want to get into the hyper-aggro end of attack which involves an ariel 2 tip and actually using an ariel 2 tip and probably isn't worth bothering with unless you're crazy or really desperate to have some small chance against defense with attack types.