i will skip first question since i dont know the answer

IMO, more difficult to mine = higher bitcoin price, almost same as gold. But this is old theory and as you can see the difficulty increase a lot this year but the bitcoin price still going down.

In bitcoin mining, the more blocks are solved the greater the difficulty for the miners so it takes a very long time to mine the bitcoin so that the total supply will not be seen to increase significantly different from mining with other algorithms. While mining does not significantly affect bitcoin prices because the bitcoin price in some marketplaces is the bitcoin holders, the miners only process assist in processing a bitcoin transaction.

1. Supply of bitcoin is fixed from the first day of bitcoin and nobody knows why satoshi have choose 21 million as total supply of coin. Supply of bitcoin is less than 21 million right now but it is increasing everyday till it will reach that limit. After that there will be no more mining reward for miners but they will get tx fee.

2. Mining will affect total circulating supply not the total maximum supply.