Hahaha yeah I have a new setup myself so i know what waiting's like ,also bleach those pebbles while you mention it then wash them off in tap water and air dry.
The problem with those stupid things is they probably have them outside or warehouses, where ever and there already majorly seeded with algy spores.
but yeah all your testing can be done in the room as well as the solution (just use tap water for the test of course)
bleach all your equipment and wipe the room down you never know what if anything is lurking around best just give it a quick wipe over bleach and water.stops things like powdery mildew mold spores etc.
Make sure you have all your equip on hand ie. ph/tds meters, "calibration solution!" etc
You will need to also find out the quality of the water you are using ,wether it be hard or soft if its mains water.
Ro is better only because it gives you a clean base to start you nutrient profile however super soft water and Ro require a Cal-mag supplement.if the ppms of your tap water are low enough and the chlorine has dissipated no extra health benefits are gained using Ro water but it is nice to have a clean slate. hope these start up tips help mate