Starting a BrickLink store is a ton of tedious work. But its work that I enjoy. If you have ever worked in a parts house, like a NAPA store, it's really no different. You won't see many customers at all until you hit at least 50,000 parts. At 75,000-80,000, things will probably pick up even more, depending on your store.
There are three ways to go. If you have access to a parts distributor, you might specialize in having a ton of well-used parts, such as having at least a few hundred of most colors of 2x4 bricks or a heavy concentration of minifigs. The second way is to try to have the widest possible selection, even if that means having only one or two of each piece. Personally, I do the third thing which lies somewhere between the other two. There are many parts in which I have 100s of and I try to have a wide selection of parts but it is all give and take.
There are a ton of other things to share but I will offer this: Find the space that you think that you will need. multiply that by 10x and you MIGHT have the space that you will eventually need. There are many YT videos to watch to get you started but, honestly, those are starting to look dated. You might try this one to get started: