I receive BC:
2.) I will receive automatically the full BC amount and as soon as it is written to blockchain it appears automatically in my "Addresses" Tab as yellow line
correct?
You will see an incoming transaction as soon as the sender signs and broadcasts it on his end. If it's valid and picked up by nodes and included in their mempools, Electrum will show it to you, but in a green standard address and not a yellow change address.
Yes, electrum allows to select which address(es) you want to spend from.
To do so, go to "Addresses" tab and right-click on any of addresses you want to spend from and select "Spend".
I prefer selecting UTXOs from the "coins" tab instead of the "addresses" tab. You can have multiple UTXOs on the same address and using the "coins" tab is easier in such situations. But let's not confuse the OP with this right now.