If I may pitch in my two cents re: this topic...
I've become fed up with these start-up model airplane shops lasting for only a year or two before everything implodes on itself. Most of these are started by young entrepreneurs, and while I appreciate the ambitions these folks have, the ones I've followed end up falling off after a while; not shipping out orders, failing to communicate with customers, storefront filled with listings of models listed as preorders from two years ago, etc.
Now I can't confirm why exactly these fall-offs occur. Part of me thinks it's something to do with school taking up much of their time, or perhaps some other conflict. Obviously, you can't work around school if that was the case, but at the same time, you would think to communicate this with your customers, notifying of an extended period of downtime due to this or some other conflict.
RM and Funny Models are two notable examples to this. Funny Models vanished as of a few months ago, initially deleting their storefront (not sure if they gave advance notice of this) but they kept an eBay store going, though they shut that down too.
Long story short, I don't think it's wise to start a business as a young entrepreneur, especially if it's an online store, and you have to worry about school taking up most of your time.