1) Is there a limit for buying and selling bitcoins for Electrum's wallet? I know Coinbase had a $3,000 cap
Electrum handles Bitcoins, not dollars. It has no limits on how many Bitcoins you can store.
2) I noticed Electrum doesn't work on iOS, I would like to use it on the go as well. How do you Electrum users do that?
I don't use iOS, but pick one:
https://bitcoin.org/en/wallets/mobile/ios/Based on my current knowledge, I'd choose breadwallet from this list.
Best practice: Store small amounts of Bitcoins on your mobile wallet to use "on the go", and keep the majority of your Bitcoins safely in cold storage.
3) How much resources does Electrum use? I am just trying to figur out what system to install it on.
It doesn't use much. Virtually any system should work.
4) It's interesting that there are so many different wallets. I was only introduced initially to CoinBase and online wallets. I had no clue about Hardware wallets, and offline wallets.
Again: Coinbase is not a wallet, it's an exchange.
I do appreciate the Hardware wallet of Electrum which I am going to seriously look into and have that has possibly my main storage wallet. Then I might have another wallet for day to day and smaller amounts. What do you guys think of Xapo for the smaller amounts?
Xapo too is not a wallet. Many people use it though. Just try a few and see what works for you, that's the beauty of so many different wallets.