You are welcome! From what you posted so far your patience and willingness to extensively research your options for a second razor have been impressive. My sense, since you returned the Tatara Nodachi when it didn't work for you, is that your focus is on realizing repeated great shaving experiences versus building a razor collection (perfectly fine if you do want a collection) and that both shave quality and tool aesthetics are important parts of that experience for you.Thank you for your reply! I can amend my last post.
Since you appear to have found your ideal razor that delivers along both these requirements my recommendation is to focus on fully mastering your new tool for the time being. Sense, from your polite responses to suggestions on more razors to consider, that you may be thinking along these lines. No need, unless you want to build a collection, to succumb to premature Razor Acquisition Disorder (RAD)
This will also, if you are not fully there yet, let you put more focus on other elements of a great shave such as building your ideal lather. Sounds line your Simpson Trafalgar T3 synthetic is working well for you and it looks line you've already found the right blade in the Astra SPs. I use Astra SPs also and they work well.
I also primarily use two synthetic brushes that also have 26mm knots (Razorock Monster and Big Bruce) that let me produce great lather from almost any of my soaps and creams. My third brush is a 26mm boar brush (64mm loft) that provides a different lathering experience (more scritch/exfoliation) and will lather hard pucks faster. Great quality boar brushes are available for under $15 so you may want to experiment with one. Mine is a Razorock Blondie bleached boar (rebranded Zenith 80N) that did not require much break-in. Note that while synthetics typically dry out over night it take a couple days for a boar to fully dry. Regardless of your brush preferences a general recommendation here is that rotating between two brushes is more ideal than use of a single brush though we often see posts here from members who've been shaving with a single brush for years.
Each of us takes our prefered shaving journey ranging from collectors with museum quality displays to those with a single razor and brush just looking for an economical shave. My primary interest has been in a great zen like shaving experience so I don't collect hardware limiting myself to the three brushes and three primary razors. In fact when I was recently gifted my Rockwell T2 I relegated my existing adjustable to use as a travel razor. I use three brands of blades including Dorco, Derby Extra and the Astra SPs noted above. If you like the Astra SPs you in your Blackbird you may also want to try Dorco Stainless or Prime blades that I've (and many here) have found to be excellent.
My primary rabbit hole (perhaps a mild case of Soap Acquisition Disorder (SAD)) has been in the area of shaving soaps. I rotate across around 16 shaving soaps and creams and have tended to acquire signficant reserve stocks of hard soaps that I really like such as Williams and Mitchell's Wool Fat (now discontinued). If you like tallow based hard soaps you may want to consider D.R. Harris (I have Windsor) and Cyril R. Salter (exact same soap base as D.R. Harris for half the price). Both are excellent and still in production. Definitely try a stick of Arko as it's the best value out there if you don't care about a fancy aroma. Finally the new non-tallow Tabac pucks are also excellent if you like the scent.
Cyril R. Salter also makes excellent shaving creams. I have both the Vetiver and Wild Rose. LEA creams (I use their Professional tube and Mendolada (menthol)) creams are also excellent and reasonably priced. If you have an interest in further exploring soaps and creams I can send you a link to some threads that will be of use as you research different options.
Overall I've found that almost any shaving soap or cream can deliver great lather with the right technique. The key is to adjust your techinque to the product characteristics or, if you only like to lather in a certain way, stick to products that work well with that method. As an example hard triple milled soaps take more loading effort that soft artisan products so shavers who mainly use artisan products will report poor results with a hard soap puck when they try to load it with a barely damp brush for just 15 -20 seconds.
Regards and let us know how your shaving journey continues to evolve. Your insights to-date have been excellent.