Hi Steve and welcome to the forum,
I can't provide you feedback on the SaleHoo Stores platform, that is of course best coming from one of our members using the platform. That said, in my opnion you should most definitely have your products and supplier/s lined up before starting any website, certainly at least have your core products ready to go.
You have to remember that you are paying a monthly fee for the website, so you really need to have all the boxes ticked before signing on or you'll just have dead money going out each month while you are still getting yourself sorted. So teh website should really be pretty much the very last thing to tick off, get all your other ducks lined up first to save yourself from burning cash.