As others have replied, you can get away with pretty much any basic epoxy. The BSI stuff does get brittle with age, but certainly will work. JB Weld makes a line of epoxy (not just the standard high temp jb weld, but regular epoxy as well).
However, if you are planning on doing more fiberglass work in the future, you can easily use this as a learning experience to learn how to modify basic epoxy (like West System 105/206 or US Composites) using fillers to become any type of epoxy you want. I started out buying specialized epoxy for each type of application, and I am slowly migrating to just tailoring my basic West System to any application. Structural bond, add high density filler. Fillets, add high density filler plus colloidal silica. Laminating, use straight up. Interior fillets, easily injected with milled carbon fiber (although there is some debate as to the effectiveness of the CF...).
>>Also should I be using a different epoxy for the motor mount and centering rings?
I do not. Some people insist on JB Weld high temp epoxy.
Regardless of what type of epoxy you use, the absolute most important step is surface prep. If the surface isn't cleaned of oxides, grease, or mold release, you will not get good adhesion for any epoxy, whether it is cheap or boutique. Also, make sure you wear proper dust protection for any fiberglass work that generates dust. Once that stuff gets in your lungs, it doesn't break down or get out. Despite all the warning, enjoy this build. After you get comfortable with fiberglass builds, it's pretty hard to go back.