I would say that with a protein skimmer and powerheads you don't need a filter at all, just my opinion. Use plenty of live rock for filtration (suggested 1-2 pounds per gallon) as for cleaning I have used vinegar because I am too afraid to use bleach or chemicals!
One it's clean you can add rocks, then sand, then water. I buy my saltwater pre made but I have heard that for the initial fill you can add salt straight into the tank. For future PWC
you will need to do it in a separate container with a heater and a powerhead to mix. Make sure you are using quality water, not tap!
I would invest in a saltwater test kit so you can measure ammonia, nitrite, nitrate and ph through your cycle. Do a bit of research on the cycle process, can take up to 6 weeks to fully cycle before adding fish/corals/inverts. You will need to upgrade your lighting if you wish to keep corals or anemones. Anemones need intense lighting and a mature, stable tank. Most suggest 8 months or more, which is good because it will give you time to get the hang of all things salt! A refractometer is also a handy to ok for measuring salinity. Before you purchase anything ask loads of questions and get advise from here, it's a great site with loads of people that have been there, done that