1. I DEFINATELY suggest playing as random, so you get to learn to play all four races. Even if you end up only playing one, you have to know the other so you know what your up against.
2. There some disputes in this area, but I'll try to post a basic start for each race. These are basic slow-teching ways to start, and differ depending on what your plan is.
Human: 3 peasents to gold, Alter and Barracks. Build peasent. 1st peasent out to farm. 2 more peasents to gold, make plenty for lumber
Undead: 2 acos to gold, 1 build crypt, alter, then send it to gold. Ghoul on lumber. 1st aco out to build a ziggurat, then to gold. Fill up mine, and when crypt is done, pump out ghouls
Orc- 3 to gold, one to barracks, one to burrow. 1st peon out to lumber, build an alter when you get the cash.
Night Elf- (this one is my preferencem but its disputed): ALL wisps to gold, first one out to alter, second to well, third to WAR. Then LOTS of wisps on lumber (you will use them later to make buildings, so you should have a surpluss).
Hope that helps!