One of the best ways to invest is look for coins that are less than $1 and invest in them. But before you do, you have to study the coins of choice and get to know about them, their development stages, roadmap and current state of the project. Investing in 2-3 coins should do in my opinion.
I personally wouldn't recommend the above, "cheap" coins are only "cheap" because there is a high supply, not because they are undervalued. The price of a coin is merely [market cap / supply = price], so either it's cheap as the market cap is very low, or like Ripple it's cheap as the supply is enormous. To put it simply: the price of a cryptocurrency is meaningless, it's only useful in the context of knowing how much it cost you. Coins with a high supply have a much less attractive inflation growth for a starters, not to mention attract investors who think they are cheap, rather than good.
I think what you suggested is very sensible, there was a short series of interesting videos about high and low risk crypto investment portfollios which you might like to check out, they are from Louis Thomas. It considered low risk to be with 66% BTC, medium risk to be around 50% BTC, and high risk to be with only 33% BTC. Blue chip altcoins are otherwise considered a lot less risky than lower market cap altcoins, specifically tokens.
Bare in mind we are also in bear market (no pun intended!), so personally I'd recommend low-medium risk portfolio, on the basis that if you want to increase the risk of your investments you could also sell part of your BTC later for altcoins, ideally when the bull market returns, rather than before.
Hope that helps, best of luck. Glad to hear more people coming into the crypto space, no doubt the low prices are attracting new investors.