Umm well those are hard or impossble questions to answer with the given info.
1. Depends on your starting costs, I would recommend finding products and then estimating that number on what would work for your situation.
2. Anyones average retail price will be different than yours. If someone is selling high end designer goods or electronics....and you sell lower end items your average retail price will be vastly different...even if your proift margin is the same.
3. Gross sales is not a good indication either because as I said from before...someone could be at $100,000 in sales but be making a 1% margin... and you could be at $20,000 in sales at 30% and be a making $6,000 which is much higher than the person selling $100,000 dollars.
To summarize this...you must 1. find out what you would like to sell. 2. Check the places/ websites you are selling on for what each item is selling for, how often the product is selling, and how often you can get the product from your supplier. You will then have avg retail, quantity, and if things go well, an estimate of gross profit. It all depends on what you sell.....