Plan 1: Buy BTC and ETH only. Spend $50 and buy 50% BTC and 50% ETH. No schedule and buy on dips.
Plan 2: Buy BTC, ETH, and LTC. Weekly, regardless of the current cost of each coin. Alternate between coins so 1 week buy 50/50 BTC and ETH. Next week buy 100% LTC. Next week buys 50/50 again.
HODL both obviously.
Also at what point is a hardware wallet required?
I would go with Plan 2. I always think that investing in Bitcoin and Ethereum is really profitable in the long run. Litecoin also seems like it deserves a chance. Because in nearly one year, the price multiplied itself around 6 times.
And when it comes to the requirement for a hardware wallet, you can prefer it when you have an amount of coins which is worth really high and you would like to secure it.