now i am a little bit confused about what you are trying to do. some things you say sounds like you just want to fork bitcoin and change some variable which doesn't seem to be teaching anybody anything but some other things you say sound like you want to actually build a blockchain from scratch which would teach you and others lots of things but it will be extremely hard because it requires lots of programming.
for example when you say "...so that I can learn about mining..." does it mean how to use an application to mine new blocks or does it mean how to actually "mine" a block which requires understanding how hashcash works, how to construct a block from its trasnactions (building Merkle tree) incrementing nonce to find the hash that satisfies the difficulty target with its zeros.
At the moment I don't even know how to lay a genesis block.
well you first set your consensus rules like difficulty adjustment, block size, algorithm, ... then create a new address and "create" the first block which is more like a hack or hardcoding it, then you "mine" the rest of the blocks from that point on.
I don't think people should have to mine 24/7, so a longer block interval might be a good idea
i think it is a bad idea because if someone wanted to learn and mine a block they would have to wait a full day to succeed! setting the difficulty adjustment to seconds is probably the best idea (similar to TestNet) it both allows people to mine blocks fast without needing to wait around and waste computing power and it prevents the coin to have any value because you can simply mine millions of blocks in a day if you wished to.