It sounds like you're getting there. I think the Simpson synthetics are very good brushes and a terrific value but try the others. I also like those Stirling soaps. I'm not crazy about Derby blades but I do like Feathers, Gillette Silver Blues, Gillette Platinum and BICs. By the way, what razor are you using?
I'm not a fan of Derby, either, but that's me. I stick with the Astra SP (Superior Platinum). You have to find what works for you.
The Merkur 34C is a classic. It's all you really need. As for your blades, you have a good selection. Of the ones you have I like the Astras, the Voskhod, the Bolzanos and the Gillette Platinums. The Wilkinsons are okay too. But of course, as with many things in shaving, it all comes down to personal choice.
Do you like big or small brushes? What is your density preference? Backbone preference? Loft height preference? Do you face or bowl lather? If you don't know the answer to all of these then ai suggest you do some exploring before you drop that kind of money. I'd gets few brushes with at least one being a nice synthetic Something like: PAA Amber Aerolite or Yaqi Sagrada Familia A couple cheaper, but still very nice, badger brushes with different characteristics. I like QED brushes myself. Remember...more expensive doesn't mean better. A lot of guys buy crazy dense brushes because of the prestige and trendiness. I've not found ultra dense brushes to perform any better or even as good as balanced brushes. Simpson chubby for example...very disappointing. Just a crippling amount of hair. Wastes soap and doesn't release lather and binds up the knot. My all time favorite badger is... QED Select Faux Garnet. Only $65 bucks. I sold all my Simpsons and $150+ dollar badgers Saville Row are also amazing and a bit more dense, but not stupid dense.
Also, try the following blades. Blade choice is, at least, as important as razor choice. Gillette Silver Blues - first choice 7 o'clock super stainless (green) Gillette Platinum Bolzano Astra SP Personna Israeli red/lab blue
Remain consistent for at least a week barring severe allergies and the like. Changing too many variables can be detrimental.