I learned to solder more than 40 years ago in a formal 2 year electronics class. My instructor taught us the importance of a solid mechanical connection prior to soldering. Whether I'm building a kit or a scratch build a little extra planning is prudent. With a kit build I'll build it stock but also think about what parts I might want to experiment with. Those components, coupling and parafeed caps for example, will just get tac soldered in place. That way it's super easy to try different components without the hassle of ripping mechanical joints apart. Then when you settle on something you like you can install it permanently.
I've been building Bottlehead kits for a long time. In the early years there were some areas where you could improve the quality of the components. Those little brown interstage caps an speco autoformers come to mind. But over the years Bottlehead has refined their designs. The prices of their kits have gone up a little but component quality has gone up a lot. I can't tell you how many times an "upgrade" that I thought would be better actually made the sound worse. But you wouldn't know that unless you built it stock first. My recommendation is to build it stock. Let it break in for a good hundred hours or more. Get familiar with the sound. Your journey might just end there. If you get the bug to experiment, go for it. Just take your time, only replace one component at a time and enjoy the music along the way.