well.. you asked a lot of "can I" questions and often the answer is "you can, but..."
you can rinse your sand with tap, but honestly you don't need to rinse your sand.
you can start with dechlore-tap water, but that often leads to a worse algae bloom during or right after your initial cycle.
you can have a 10 gallon SW
setup, but if this is your first SW
tank you may very likely end up frustrated as you are still going to be learning and developing good SW
care habbits while battling the chemistry in a small SW
: Upgrade to at least a 20 gallon tank. You can keep everything you've got so far so nothing will be wasted, you may just need a bigger heater and a little more sand (depending on what you have). You can keep the 10 gallon and use it as a sump/fuge for your 20 gallon. I would really suggest a 55 as a better starting tank size, if you can swing it, I highly recomended.
Don't rinse your sand.
You're going to want RO
or filtered water for water changes and top-offs anyway, so either find a cheap source (grocery stores often dispense RO
water) or find a reasonable filter and use that.
Mix your first batch of saltwater outside of the tank, (get a rubbermaid tub, very cheap, and very handy). I have a 30 gallon tub i use to store RO
water so I always have some on hand. Put the sand in your tank while it's dry, then add you're pre-mixed SW
into the tank. put a plate or bowl into the bottom of the tank and pour the water into that, it will minimize the amount of "stir up" you get when first putting the water in.
then run your cycle (please read our article on how to run a fishless cycle)
the best advice I can give is to be patient. Cutting corners (like using tap water) only ends up in more work later on and so isn't really a short cut. You have to be patient with SW
setups. They are slow adjust, but quick to fail. You have to give the tank time to adjust to any change you make, be it adding new critters, changing the lights or salt mix, etc.
keep the questions coming, it's what we're here for!