As long as they are completed in the same day they won't charge multiple commissions however they will charge multiple commissions if more than one trade is done. This is in regard to Scottrade, so i don't know the policies of of other retail brokers.

I varies with brokers. Scottrade charges the same commission whether you by 100 shares or 1000 shares. Some full service brokers charge a percent of the trade. I'd advise using a low cost on line broker to a full service broker if you are trading stock. Scottrade charges $7.00 flat fee.

Usually brokerage firm charge you a fee for the order regardless of how it is executed, but depending on where the order was executed, if there order was done OTC or it was a penny stock you mayl be charged per execution since most ot the trades are done X-clearing.

If you think that an extra $3 fees will have a major effect on your profitability - you should not be trading junk stock

No. partial fills are paid for parts of the commissions.

if ti was a single market order, he commission will be charged once.

the first lot's net cost will be slightly higher than the later lots.

No, as long as completed in same day.

I ordered 300 shares, and because it was a smaller cap stock it filled partially in increments of 100...so does that mean I will be charged commissions x3? If so, that isn't very good news, it's not terrible I geuss. Just going to take longer to get in the profitability range.