Question about "mining" in bitcoin
Mining is the process of extenting the chain with new blocks containing (or not) new transactions. The block reward and any tx fees for that block goes to the miner, who found  a nonce such that the hash meets that block's difficulty target.
In Bitcoin the difficulty retargets every couple weeks I believe. This means that if more miners start mining, they will indeed cause blocks to be found faster than the 10 minute starget on average, until difficulty retargets, where it will go back to about 10 minutes (and possibly go up or down depending on whther new miners arrive, or existing miners leave).

Due to thus two weeks retargetting, there should be only minimal change to the expected time of the last block reward (accumulation of each two weeks period's drifts).

Last, the number of txes do not influence the number of blocks. The miner does get a bit more due to the tx fees, but whether blocks are full or empty or the the middle, the target is still 10 minutes.