Start with SSB1 first! You can skip week 1 of SSB1 if you already did week 1 of SSB2. Then do SSB2 followed by GB.
You can’t rush your fitness and cramb training. Follow the progression of SSB1 & 2, Build then Specialty. You can race as you go through each one of these phases, just add a taper before each race. Each phase builds on itself (Base > Build > Specialty), so it’s not a rush to get to the Specialty phase. You’ll see you’re biggest fitness (FTP) gains during Base and Build. Specialty is simply refining the minor details, but it’s all for not if you haven’t built a foundation of fitness through Base and Build.
You have to consider your fitness long term. So where do you want to be year over year then plan accordingly. The TR calendar is great for that. It appears you were a bit unprepared this year, which is fine as you still have plenty of time.
If you were a beginner last year, realistically you’re not likely to be overly competitive moving up this year to Sport. Unless you were on the podium a bunch of times in your Beginner Cat races last year, and had a solid off season training plan (which it appears you’re starting late), be realistic with your goals. This year should be about building fitness and learning about competing which is likely to be significantly more demanding than the beginner Cat. Typically your races double for Sport Cat in time/length (more laps) and your competition likely takes their off season seriously. So set yourself process goals this year to ensure you’re moving your fitness forward while keeping motivation high and expectations in check.
I was Beginner Cat in MTB XC for 2017 as my first year riding. I had decent results with a few podiums to include a 1st place. In winter 2017/2018 I bought a trainer and Zwifted with semi-structured plans. I moved up to Sport Cat for 2018 and finished the first few races mid pack amongst the fast 40-44 category. As the season progressed I learned a ton and trained better while grabbing some podium finishes.
I found TR mid July 2018 with a few races remaining in the XC series. I made a lot of early training mistakes by not following the training plans correctly. However, I figured it out this past fall after listening to every TR podcast, reading a bunch of good books and spending lots of time on this and other forums. My FTP has gone from 193 (2.3 w/kg) in July 2018 to 287 (3.7 w/kg). I still have SSB1 & 2, GB, and XCM Specialty to go through as I plan to peak for a MTB 100 in mid September after my XC race season. So I expect to be very competitive this year in the XC Sport Category. Obviously I’ll be training through my XC races as I work to improve my fitness all summer.
So I’d recommend training in the TR recommended progression and you’ll be crushing the Sport Cat soon enough ♂