First post ever!!!

Hello Fools,

I'm new to investing and have some questions about how to actually go about building my balanced portfolio. I've watched some of the investor roundtable vids and read some of the basics (realizing now that I've already made a silly first mistake by going "all-in" on my first stock buy...whoops).

As someone who plans to invest small, maybe ~$500/month. How do I go about building a diversified portfolio without getting hammered by commission fees from online brokerages. My thought is, if I want to avoid fees, I'll have to buy one stock at a time and that makes me highly undiversified. Or, say I want to commit $3000 of my annual $6000 to LinkedIn (to make the Gardners happy) -- how do I spread out the rest of my investments without getting crushed by fees.

Also, how do I factor in my 401k into my overall investment strategy? I commit x% of my salary (through post-tax Roth contributions) to a target retirement date fund.

Thanks for any input you might have and looking forward to contributing in the future!