With your profit margins, it is really up to decide. if you want 10, 15 or 20% or more. What you must realize that it is a very competitive market especially on online auction sites.(eg E-bay). What you can do is use Salehoo Research lab to find product that do well with product that interest you. Complete an in-depth market analysis on those products so you can ensure that you are competitive and that you are on track to reach your GP goals.
If you plan to start out with drop shipping, think of some products that interest you and you can make some money from. Best bet would be to find 1 supplier that you can build a good business relationship with gaining better purchase discounts over time. As time goes on you will gain more confidence with trading and you will want to spread your wings to other suppliers to extend your product range and gain better prices. If you throw your self in the deep in with a lot of products and alot of suppliers, you will stress your self out to the max by managing mutiple customer orders, warranty claims, Refunds / Returns as well as after sales service.
Keep it simple to start off with and build from there!
I have considered a retail store myself but it is a long time goal due to the necessary requirements needed to make it successful. Thing like right area location where there is high traffic, lease and rent, wages and other overheads, costs involved setting shop, all your money will be held in buy and hold. plus other things like advertisement, business registration. a lot! lol :p
If you are drop shipping you don't have to worry about breaking even as you have no inventory. your estimates of how much money you would like to make are very reasonable but you would have to devote your self full time to get there in that space of time.
It is good to see that you are very realistic as drop shipping will not make you rich over night nor will it replace an income immediately
Everyone at Salehoo is really helpful and we give you the necessary tools you need to make your business a success
Hope this has been of some help :o)