I like to have 4 good set ups and 4 tanks and each one has 1 ouf my 4 favourite Juice. I am very particular and wont Vape a juice I am just so/so about........It MUST be something I cant live without and a flavour I am fully addicted to otherwise Id forget to Vape

So seeing as I do at present have 4 I would likely murder someone for them if i had to.. (j/k) I have 4 set ups.
If I had 8, Id have 8 set ups simply because i cant be bothered to change tanks, etc. I work at home and always have 3 all on at the same time on my desk and go between the 3....I am however, an addictive personality

Plus, its just fun buying new ones all the time...But as I say that, I am also of the belief that it is best not to keep buying if you arent happy with one when everyone else is...I would keep at it until I got it to work properly rather than buy a new one.
I'd rather have 1 set up I loved than 4 I didn't.
Best answer to your question is what feels right for yourself!