Even 3 letter .mobi is hard to sell, even at a cheap price. Ones that are sold are either generic or luck, or just by master domainers, who know what they're doing. I'm not one of them, so I got lucky. It was cashexpress.mobi.
If I could give any tips to a first-day domainer, it would be to keep reading, and you'll get all the info. Read dncollege. Ask questions, just like what you're doing.
Veterans keeps saying "stick to the .com". I find this to be true. One master told me to wait till you make a million dollar sell with a .com first, then you can invest in other dots. Once you can make your first $1m sell with a .com, you'll be experienced enough to buy other dots and not waste your money, master says.
So, according to this master, make your first $1,000,000 sell with your .com. Then, you can invest in .mobi or any other dots.
Yes, master. lol