That's a smart thing to do. Diversifying your portfolio. Don't put all your eggs in one basket. That's what they say. Go look at https://coinmarketcap.com
I consider top 10 cryptocurrencies as good investment options especially Ethereum.
Ethereum is undervalued but good to hold for long term because it has a good future.
Bitcoin cash is good also. Better keep it. Keep Bitcoin also. Maybe 50% for Bitcoin and 50% for altcoins since Bitcoin is really dominating the market and altcoins can fail. Here are other good altcoins to invest IMO.

1. Iota
2. Neo
3. OMG

Good luck.

You mean using the same private keys? Yes you are essentially using the same "wallet". Another way to thank about Bitcoin is really you are not holding any "coins". All that you are "holding" is in the blockchain which you control through your private key.

You should not keep your back up of your wallets only in web based services like cloud of mega, google etc. You should keep a few copies of these back ups in some usb-s cd-s and other good storage device. You can opt to shrink your hard drive and create a small partition of 10 GB only to keep all your back ups.

It the private keys can be obtained from the wallet files, however you would need the password (assuming that you encrypted the private keys, which I would highly recommend) to actually obtain the private keys.
*Edit: Grammar

You should be good. I’m assuming that the “Linux Laptop” is the mostly offline computer of yours, otherwise there would be a risk of hacking/malware obtaining your private keys. Regardless, it’s still a pretty foolproof setup.

The best way to get secure cold storage would be to:
1. Download a linux distro and burn it to a CD
2. Download a copy of walletgenerator.net and put in on a thumb drive
3. Boot up the Live CD, insert the thumb drive and generate a paper wallet (if you plan to keep a digital copy be sure to add a password to it and keep the password on paper)
4. Print out your wallet or save it to your thumb drive

If you follow those steps you’ll have a very secure and easy to use cold paper wallet.

Yep.  For that kind of purpose, Jaxx would be ideal.  You could also try depositing some Bitcoin that you bought into an altcoin exchange like Bittrex and then withdrawing from there into your wallet, which would avoid potentially high fees from Jaxx (I think their fees are 1% or something - integration with Shapeshift).

Well, you can use coinbase if you are scared that you can lose private key or something like that. However, I suggest you should use electrum and myetherwallet

Not really.  Jaxx is good for someone who uses multiple coins on a regular basis, but if you want cold storage and long-term storage you'd be best off creating separate paper wallets for each coin.  You could have the paper wallets in safes, bank deposit boxes or buried, to give some examples.

You could also try using a TREZOR with multiple passphrases including a decoy.  Then you're quite safe from 5-dollar wrench attacks, hacking and nearly any other problems I can think of.  

I'm pretty sure you can store Bitcoin and Ether in the same TREZOR, using MyEtherWallet as well as their regular one.

It all depends on the level of security you want.  If you get Jaxx it will probably be okay, but you're susceptible to viruses and you might not know if something happens since you wouldn't be accessing it regularly.