Online investment accounts - strategy?

[Buffalo]

Say, for arguments sake that i had $5000 and I bought 10x $500 of shares in various outlets. I have two questions:

1) What sort of spread should i have over business categories for a pretty decent growth rate (i can afford to lose it)

2) Assuming my returns go up, what would be the best to do considering I am starting with a small amount (I don't want to put too much into this yet as i have never done it before, so want to have a bit of harmless fun for a bit and see if i can make any money)? Keep the profit in the originally chosen jars to capitalise on the gain until they start to decrease or I find a better offer? Or, cream off the profit made, say every 6 months and use it to add new shares into the portfolio, i.e. get 11, 12, etc companies instead of the original 10.

Thanks ~PHIL