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.
I will go with Plan 2 with this with a bit of a change. Maybe you can buy 50/50 with ETH and LTC and then the next week 100% with BTC instead of what you said. Plan 1 can work too but diversifying your money into different coins would be better especially if you have a huge amount of capital. If you have a small capital though then Plan 1 would be better.
Also at what point is a hardware wallet required?
When you are thinking of a long term. For ex. you want to hold Bitcoin or Ethereum for a long time (minimum of 3 years for ex.), it would be better if you will store it on a hardware wallet because it is more secure there therefore nobody can hack your coins.