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this is understandable I will use 132 bits of entropy as a string plus the increments for extra security and uniqueness plus it would be deterministic for me if whenever I forget I can recover it however the big number is just hard to recover if lost so the point stands that I will use string, not my name as I gave that just as an example I will use a string with 132 bits of entropy as that is strong and used by electrum as well plus by using GPU I don't want to save all those billions of addresses so i will only save the addresses that match the pattern but with my method of string+n increments and for this increments are necessary if you use same string billions of times it will generate the same address but if you add the needed numbers/increments it will fulfil the task of pattern and uniqueness since using 132 of entropy for single address is not very economical I would say.
A random string with 132-bit entropy is much better than what I initially thought you were doing (
just make sure you add the string at the end of n and not the other way around), but in my opinion, if you really want to generate private keys this way then I suggest ditching hashing functions altogether and use
Scrypt for your algorithm instead, which can be tweaked to make brute-forcing infeasible.
SHA256 is secure you are declaring that sha256 is insecure? besides that length-extension attack wouldn't work on anything which is considered secure such as 132 bits of entropy anything else other then that would be going far from the topic as per the rules of the forum we should stick to the main keywords here SHA256 WALLET AND BITCOIN and what's between the first post.