and I'd like to find a good Monero Wallet to use with my Hardware Ledger Nano S on my computer
Both the official CLI/GUI wallet and Feather wallet work with hardware devices. The Monero subreddit is a good resource for Monero info:
https://www.reddit.com/r/Monero/as I assume to date it's not possible to send or receive cryptocurrency via a iphone or android device?
Ledger Nano S devices are not compatible with phones.
how exactly do I use a Bitcoin ATM alongside and Electrum Wallet? I use a hardware wallet too btw.
You can use Electrum to interact with your Ledger device by following the guide here:
https://support.ledger.com/hc/en-us/articles/115005161925-Set-up-and-use-ElectrumOnce you've created your wallet, it's a simple as taking the next receiving address from Electrum and sending coins which you have bought to this address.