If your worried about the spread from OTC retail brokers trade the currency future's through a commodoties broker you pay commission per trade but no spread other than what market feed bid/ask gives.
As for scalping theres a couple of reasons most retail otc brokers dont allow it 1 being its very risky and 2 being it clogs up there servers and doesnt allow fair use for other non scalping traders.
Anything under H4 is scalping for me, the longer TF chart is more like investing not gambling especially for something like the dow which I trade the daily chart gives much better results with less broker commissions and stays out of the spikes which will whipsaw you to death.
Honestly have you ever seen a whipsaw spike on a daily chart?
One of my broker's is an ex cbot floor staff commodoties trader, specializing in futures options, who manages million in accounts per year, and he told me off the record that he never even looks at a chart under D1.