As Wholesalelist has said, not an easy road you have chosen, not an easy road at all. There is always plenty of people happy to take your money by telling you they have 101 secrets to making you rich on ebay, but they are the ones that end up with the money.......your money!
I'm a Powerseller myself, even though ebay to me is just a part time side issue. I sell 99% secondhand items myself, things that I source locally through garage/yard sales, weekend markets and auction house sales.
I don't focus on any particular products, just the price of the products. I find that secondhand gives me better bang for my buck than any new product can even come close to.
Quick example, went to a police seized goods auction yesterday. Just bought a few top up products. apple ipod, auto sony cd, 6mp sony digital camera, lg chocolate mobile, two as new football jumpers and an RC helicopter and car.
I spent just under $200AUD, with past experience in these types of products showing me that I will make on a slow market at least 100%, but if there are buyers around I have the potential to make around 200-250% on my small investment.
The most important advice I could give you about selling online is to sell online, and online does not mean just sell on ebay like so many people seem to think it does.
There are a stack of sites out there where you can list items, most for free with a charge on the sale only. OK, not much traffic, but if you cover enough bases then that traffic all ads up, and until people start using these alternative sites they will never build up their traffic, so help yourself in the long run by not just using ebay, but every online avenue open to you to maximise the potential of a sale.
If you combine that marketing resource, with an open mind. A thought process that keeps you thinking outside the box as to what you can sell, and where you can find it, even places like charity shops. These, along with other product resources I mentioned before are worth their weight in gold!
Good luck with the venture.