Switching between Fighter/Gerwalk/Battroid isn't difficult, but I wouldn't do it too often only so that the joints can hold up when you keep it posed over time.
The build wasn't difficult, if you know how to build a model and use waterslides you're fine. It's just that with painting something like this NEEDS masking and an airbrush with all the fine lines and paneling you have to do. Luckily it is eased with the number of waterslides you get with it.
It's a typical Bandai kit, it's pretty solid but it's not cheap like the Omegamon I posted in the Gundam thread a while back.
I would refrain from buying this one and waiting. When I found out that Messer/Arad were coming out as well as Hayate's VF-31 with the Super Pack and Keith's Draken, I low-key regretted my purchase for this one so early and should have waited.
These are definitely my future purchases because I don't want to miss out on them later...