Welcome to the hobby
I would say go with the ro water from the store. Just ask them how often they change there filters. The di filter just removes anything that is left over from the ro.
For salt youwill get varied opinions. I used to use Instant ocean and switched to tropic marine as it is higher in calcium,magnesium etc.I think that is just a preference. I have never used the others so i can't comment on that.
Have fun