Don't be afraid of using your 10 gal for saltwater. Its a way to learn. I had mine set up for 10 months before graduating to a 55. Just keep 2 small fish in there with some hermits and snails, a chunk of LR and some sand, a filter and a small powerhead. Do a small water change every 2 weeks and top off with purified water every day. The only issue is lighting. You can use the 15 watts it came with, but not much will grow. Change the light to a 10k or 50/50 bulb and you will get moderate growth. Buy a 50/50 coralife light and more will grow (on the LR). I kept 2 clowns in mine and everything went fine as long as you go slow, read a lot, and pay attention to it.
ps - when you fill it, use 10 gals of purified water from Walmart or where-ever. You'll reduce the phosphates, no chlorine, and it will start you off better than using tap water.