If I knew you were going to stick with the hobby until at least the year 2020 I'd say just save your cash & pull the trigger on a 16"
However.....The 8" would be a start I guess. My first 8" experience went thus: First night out I said "is that it? Ok well, I'll be building a bigger one!" Which I did...A 12.5".
Aperture fever is nasty
