Skills that allow you to buy and sell things remotely: Marketing, Procurement, Daytrading, Visibility.
Skills that increase maximum number of active orders orders: Trade, Retail, Wholesale, Tycoon.
Trade skills can be divided into four groups: With more money you can invest in more items making you more money. While this isn't true during hauling, good hauls tend to be fairly short and you can always dock up halfway through.
Time-flexible: A lot of trading happens while docked up, and it's easy to go AFK with no real danger most of the time.
Easy to do during war: With a small investment in skills (Marketing, Procurement and Daytrading to level 2) you can easily station trade in one system while docked up in another, or use an alt to trade in other ways.
The only skill you really need to start with is Trade, without which you'll probably feel a little limited in the number of orders you can have open.
Easy to get started: You can start trading right away on a character with no skills, and the amount of skill training needed compared to other professions is fairly low.