First of all I wanted to say that I am completely new here and therefore I am not sure where to exactly post my questions but I hope I am at the right spot...
So i decided to jump on the Bitcoin train aswell but unfortunately too late and instead of 2400euro/btc I had to pay 2800euro/btc. At the moment I don't want to use any hardware wallet and therefore I had to create a wallet as secure as possible because otherwise I am always scared about virtual theft and I have too much to lose. I created a bootable USB drive and downloaded the newest tail from the official website, I verified the version through the firefox addon and furthermore through Kleopatra and some SHA-256 Hash (instruction from the internet) but I heard there are still ways to have downloaded a infected version through something called man in the middle attack, is that possible or am I just paranoid? After that I booted from the USB and had my WIFI turned off the whole time and created a standard wallet in Electrum, encrypted the persistent storage and Electrum and wrote down the seed words on paper. I created a watch only adress with the public key from Electrum to watch transactions. I already sent some amount to my public adresses and recieved them successfully but my balance on tails obviously shows 0 because it was never connected to the internet. What I want to know now is that how am I able to restore my wallet from any given computer if my seed words have been created offline and therefore have never been able to be sent to electrum servers? So how do I exactly verify that I own the coins without connecting my offline wallet to the internet?  Furthermore I wanted to ask if my wallet is 99.99% safe from any virtual theft since my intentions are to hold btc for long term purposes? Also in order to satisfy my mind that I will always be the owner of my btc I need to know what will happen if Electrum somehow vanishes and all the servers are shutdown how will I be able to restore my wallet from the seeds because no other program except Electrum would accept those seed words and only if they have been transmitted to the internet before, right ? So basically I need to understand the concept about the way I actually stored my bitcoins and if it is safe enough for 5-10 years from virtual theft or any problems that might occur if electrum servers are shut down?
I would highly appreciate any help and sorry for my bad English in terms of the technical explaining but I am from Germany.