The solid mounts help keep the engine from moving when under load. Guys on this forum offer mixed reviews. Some say that they are a must, some install them only to remove them. The main value-add for the solids is that they don't bust and leak fluid like the hydraulic ones do. The solids don't need replacing. Where as the hydraulic ones do because they will bust at some point. The main complaint for solids is excessive vibration, as the solid mounts don't absorb them as well. I'm in need of a engine mount as well, and after some thought I'm going to install the hydraulic mounts. I personally prefer the smoother ride, and limited engine vibration.
I strongly suggest doing the front and rear seals. Absolutely. There are countless threads from noobs asking for help identifying a mysterious coolant leak around the passenger side. It's almost always the front seal. And I know that the rear seal goes out as well. Not sure about the seal driver tool....
As far as the transmission kit, you either install all of it, or none of it. You can't really install parts of it. You could in theory, but you just don't. So not sure how to advise you on that one. I guess just put the whole thing in.
