to answer your initial question - buying TT for JT isn’t crazy, but you’re almost definitely going to end up using it for lots of other stuff.
i’m in a similar boat, but reversed! 7u x 84hp, roughly 75% full. i was attracted to TT first because of how many different functions it could pack into my system (particularly sequencing, random, s&h, and JT once i got JF), but i was also a little wary of all the coding. i got JF roughly 6 months after TT and i’m glad i had time to learn the ropes before leveling up. the learning curve with TT is steep, but after you’ve done the studies once or twice and start coming up with ideas on your own, the functions start to stick in your mind. i definitely don’t fully understand a lot of stuff going on in the code exchange threads yet, but i know enough for TT to be a capable brain for my system.
it’s definitely less hands-on than either module, but for what it’s worth TT can definitely perform the functions of both marbles and rene.