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'll definitely go with Plan 2, that's how you diversify your investment buying different coins and holding but you should at least consider your market price when you were buying. Moreover, choosing plan 2 will minimize the risk of losing all of your investment since it is divided and invested in different coins. You should consider also where would you invest more than the other coins, at least 40% would be allocated to your main coin. Well, it's your choice on how you will plan your investment and I highly recommend using a hardware wallet in case you want to access your wallet anytime.