Good luck,hope all goes well.
If you going add fish to that new an aquarium even though adding bottle bacteria,it would be sensible to get a reliable amnonia test kit at minimum but nitrate also to show that the nitrogen cycle is indeed taking place.
As what i read above you say was going get some dry rocks and place in 2 small buckets without heaters as garage is warm enough.no mention of power heads so no flow but couldnt see you say you actually ever put any rocks in any water to start cycling so if you starting off with dry rock and adding bottle bacteria its good idea to test for amnonia which is toxic to fish just to make sure amnonia not in toxic levels to harm or possibly kill your fish.
But some actually use dry rock and add 0 bottle bacteria and cycle with fish ( which no need to do these days) but need to know tell tale signs of fish in distress from amnonia etc and do water changes when needed or test is easiest
Edit: just re- read you say above you have some live sand,maybe sometimes you have some die off from live sand and produces amnonia also from the 2 clownfish, either way reliable test kits still advised ^_^
