I am a long term HODLer ~~ currently, all my coins are on an exchange.
This means you've survived several exchanges that disappeared already! You're very brave keeping them there, I'm already scared when I have a fraction of a Bitcoin on an exchange for just two days.
In case it isn't clear: this is my way of telling you it's very risky, and you've been lucky so far. Don't push your luck.
So I have a ledger nano s, which is where I keep my BTC and a couple of other coins, but it does not take all alt coins. SO I am stuck with the option of keeping them in the exchange or go to another wallet.
There isn't a single method to keep all possible coins. Your Ledger will be a good start, use it for all the coins it accepts, and find a different solution for the rest. That's what I do: I use different options for different coins too.
I know these have desktop wallets, but I am not sure how safe these are. I have heard that you need to delete app data? But then I also heard someone did that and lost all their coins.
Deleting data sounds like a good way to lose your coins indeed, if you don't exactly know what you're doing.
Ideally, desktop wallets would work great because I can at least keep my seed offline on a USB and only copy/paste it over when I want to check up on my funds or eventually sell out, but how safe is this really?
This is not safe at all: keeping a wallet offline doesn't mean keeping it offline just 99.9% of the time, it means that wallet has
never touched any online computer.
Also: don't rely on just 1 USB-stick, those things can break. Make multiple backups.
SO. I guess, is there actually a super easy way for me to create paper wallets for like 20+ different altcoins?
Or can I just use desktop wallets and just make sure the seed isnt stored anywhere?
There's another side to this plan: you'll also need a super easy way to sweep your paper wallets in the future.
I've actually been thinking to make an overview of different paper wallets, just to convince people to keep less money on exchanges. 20+ would be a good start!
For Bitcoin I trust
https://www.bitaddress.org/ and
https://bitcoinpaperwallet.com/, but by all means, don't just believe random people on the internet posting random links. Do your own research, be paranoid, and use that to stay safe.
There's also
https://walletgenerator.net/, which supports 158 different coins, but I don't know if it can be trusted.
How can I make my desktop wallets safe if I choose that route for my long term coin hodl?
You should seriously consider setting up something offline for long-term hodling.
Just get the apps, move the coins, get the seed, store offline on a usb and then delete the entire app including app data?? (will that make me lose my coins, considering sometimes it asks for a seed, but also a password when unlocking the wallet or to send coins?)
Unplugging your computer from the internet, then creating super-secret-private-keys, deleting them, and going online again is not safe. You should
assume your computer is compromised, and malware will patiently wait for you to go back online.
It depends on the wallet what you'll need to backup. For Electrum for instance it's enough to backup your word seed phrase once, for Bitcoin Core (HD) a one-time backup of your wallet.dat file is enough, and (to give an extreme example) for Byteball you'll need to backup it's complete data directory again after every Blackbytes transaction).
**Note, I am not able to run Ubuntu and all this other stuff, I just want a simple method without going matrix level and using multiple PCs, as I don't have the time or spare parts.
Have you tried Ubuntu? If not, you should at least give it a try! Download it, burn a DVD, unplug your internet, start your PC from DVD. It's quite complete and easy to use, including printer installation. Then copy the paper wallet generators to an USB stick and use them offline (with your curtains closed).
Basically all you need is a DVD, you don't need a spare computer. And yes, it's very annoying having to restart your computer each time you want to do something related to private keys, but it makes me sleep better at night
"Time" shouldn't be a concern if you're a long-term holder. It took me a long time (of postponing) before I improved my setup, but in the end it's worth it. What's a month on 5 years, right? Once you have it working, print as many paper wallets as you think you'll use in the coming 10 years. It's a one-time job. Use a cheap (=no storage inside) laserprinter (=better quality if it gets wet), and if you're truely paranoid, destroy the printer once it runs out of toner.
Remember, it's better to spend way too much time being careful, than losing your coins due to some stupid mistake.
Any help greatly appreciated, and if it truly is simple to understand and solves my problem for a good long term 5 year hodl and is safe, then please leave your address and I will donate some btc to you for your trouble.
I've seen many newbies lately offering rewards for help. And as much as that's appreciated
(my addy is in my profile > click my name), it's not required to get helpful answers.
I wouldn't try to find 1 solution for all your coins, try several solutions that cover as many of your coins as possible.
One more thing: leave instructions for yourself how to use your backups! I've seen many threads lately from people asking what to do with the 21 words they found on a piece of paper from years ago, and that's for Bitcoin online.