Low Index ETF recommendations?

I have VOO VNQ and REET into my Roth IRA that I max out every year

I’ve been keeping my money in Marcus savings for the longest time and finally realizing I’ll get much better return investing it into stocks. My plan is to invest into low index ETFs for the majority of my money, and gamble a bit with 10-20% of it.

For now, I am looking for recommendations for low index ETFs. I’m going to do my research but thought it wouldn’t hurt to ask here as well. I’ve heard of SPY and VTI being pretty good. I’m also wondering how I should diversify and when I should go about buying these shares. I know I should buy when it’s low but I haven’t seen some of these drop much. Maybe I just need more patience.

I’m new to this so any advice is appreciated. Thanks!