Definitely a flatpack and full kit makes your life easy with a first time build. Highly recommended way to dip your toes in. Plus there are lots of people able AND willing to chime in with helpful tips along the way. I couldn't have finished my NX-Studios without a few of them to guide in avoiding pitfalls.
Finishing a cabinet is actually kinda easy if using automotive paint. It is daunting to learn on the fly, kinda spendy for materials and definitely has safety hazards to work through; but if you're willing to follow the manufacturer's instructions and pay attention to the details you can easily work your way through it. Plus the longevity of the finish is very very nice.
I would defer to others on veneer, but I can help you through the paint side pretty easily.

I just finished painting a set of Triple Threat for a friend, and currently in the garage painting an amplifier chassis waiting for paint to dry.
-Lloyd