There are many things which can be done and do help. I'd suggest doing it in more than one step. Sonnax sells several helpful items for the VB, those I'd leave for when you are more familiar with the various parts. I'd do the solenoids and the filter, even the EPC solenoid if you can patiently get it out, and in. The large nut and the VB etc are in the way, so the VB definitely has to come off to do the EPC.
I'd do a J'Mod later which is a good VB shifting upgrade, which includes doing the accumulators and springs. Just the solenoids will be a decent task if you haven't been into a VB before, and if the trans is still working okay, do that now and take a breath to do the rest with more planning. The J'Mod needs some research to "guess" what your best drilled hole sizes should be. That takes time and a lot of thought, online sources will be example done on Thunderbirds etc, almost nothing to show what it does for a heavy truck. There are several Sonnax parts that can be replaced in the VB, those take some time and patience to install as well. That's why I say it might be best to do the more in depth stuff after doing the basic filter, and solenoids as possible, which are quicker things to do.