You can use either or both of those rocks if it appeals to you, though you will want to thoroughly clean all of them due to the possibility of unknown chemicals and such since they were in your backyard. For plants the sand would be good but you'll most likely need some kind of root tab since sand is inert and doesnt hold nutrients well. As for UV
sterilizers, depending on why you want it you may or may not get your desired results. For helping to prevent bacterial infections keeping already clear water clear, and killing waterborn algae its pretty good, but it wont fix issues completely, thats the job of the hobbyist. I had the Green Killing Machine and really like it, it worked well until it unexpectedly died on me. I still recommend it though, as this isnt the case for most.
Just curious, why was buying the sand a newbie mistake?