I bought an Electra used on eBay and replaced the rear wheel with a seven speed hub. Works great.

My son had a used Marin Hidden Canyon. Great bike!

I would ignore the front shock issue. The front shocks that ship with 20" and 24" kids bikes are non-functional - hardly gushy! They don't move. Seriously. A sixty lb kid won't move any shock on the market!

I would avoid mixing coaster and hand brakes. Pick one approach.