I am considering holding Bitcoin for the long term. I have learned a few basics about the blockchain and BTC mechanisms, but still unable to find a complete guide on how to safely store bitcoin.

1) How to generate a private key safely? Online tools are obviously undesirable as they might keep a back door on all keys generated. Similar reason for any library or packages even they operate offline (I cannot check if these keys generated are in fact following some predetermined sequence).

I can use a random number generator on an offline PC. But I am not a real 'hacker' and have concerns on whether any programming language can produce truly random numbers that cannot be reproduced (or say predicted) on another PC. They might all rely on some external factors (such as time) which greatly reduce the possible key generated and make brutal force algorithms possible.

Currently, I can only think of throwing dice for key generating but that cannot scale.

2) I do not want to use any 3rd party software as a wallet. Suppose I just store my private key on a piece of paper and later transfer coins into it using exchanges. Would that be a valid transaction and allows me later to spend these coins? Is there anything else I need to store together with the private key (like the hashed transaction number in transaction_input in the blockchain? ScriptSig?) I really want to avoid 3rd party software because it might be obsolete in the future and data can be degraded. (Say if I use some sophisticated cold wallet, I may experience hardware degradation in  10 yrs, no one at that time used this software, programmers 10 yrs ago cannot be reached, and any trick in coding or encoding in the original version becomes obsolete. I would be a consumer rather than an investor of BTC...)
 
Any advice?