That's pretty much what I do. I've been rethinking my etf strategy though. If you're not outperforming the S&P (which I'm not) what the fukk is the point of having multiple monthly investments? Maybe you add a bond or two as a hedge against a crash, but rather than have multiple stock ETFs it seems better to just buy a bunch of SPY, or maybe that total market vanguard joint, I think it's VNQ or something like that, only.
LOL, bad move and this is why so many people were crying bloody murder when the market corrected itself - it sounds good, but SPY/SPX diversification is not the proper diversification and leads you wide open to a bevy of issues.