In Bitcoin, transactions generally¹ have immutable self-contained outcomes—they boil down to a list of inputs spending existing UTXOs, and a list of outputs to be created. All the amounts involved are independent from the position in the block, or even what block a transaction gets into.
In Ethereum, especially transactions interacting with more complex ...
No, in Bitcoin most miners simply choose the transactions with the highest fees.
The order of transactions just has to be valid (eg, transaction that spends a UTXO of another transaction in the same block has to be placed after the transaction it spends). As long as it is any valid order, which particular order is not particularly important.
Mining is getting harder and harder every 2016 blocks (difficulty adjustment). Good mining hardware you see today is dedicated to bitcoin only. Back in the days it was profitable to mine on a pc but today you will see more than the mined bitcoin back on your electricity bill.