Good move on taking precautions.. But if i were u, i would
Use the moolah on test kits or something worth while..
The live sand that u plan on buying is a waste, u might as well use dollar bills to roll-up doobies..
The only thing that makes that bag of dirt 'live', its the microbial colonies..
its the same thing u have On and inside lr.
Lr offers more beneficial microbial processes and energy cycling processes,(at this stage). of which are ideal for deminishing initial nutrient overload..
I can pretty much assure u that the lr will give u a little spike.(enough to start cycle). if that doesn't work, u can take the raw shrimp aproach...
IMO, Ls will only give u undesirable organic levels.. which may eventually turn into nitrogeous compounds resulting in algea growth or the accumulation of excess nutrients in sandbed..