Ans, 2: Mining altcoin require low cost? Isn't it the same with bitcoin? I no sabi if the two get difference, if altcoin mining materials dey low, then we move to altcoin but the problem be say, we go fit make profit from mining altcoin?
You are right, to mine bitcoin, graphics cards like Nvedia and AMD that can be connect in grid to make up mining rig for bitcoin mining are no more profitable to mine bitcoin, but still possible to mine some altcoins, I am not sure about the strong altcons like ethereum, litecoin and others in such high categories. For bitcoin mining, ASIC like Bitmain antminer S19 will be needed or any other good news ASIC like the Antimer T17 which is also efficient.
Ans 4: If the miners go agree to lie for checkpoint/boarder say him dey come for any other purpose except crypto purpose, then it's possible for them to come. Money is everything about mining, these peopleware too are supposed to be taken care of for them to setup and install every equipments.
In Nigeria, CBN ban bitcoin, bitcoin is not banned in Nigeria itself. So, anything related to bank trasactions with exchanges and other such crypto organizations is what that was banned. Mining equipment importation into Nigeria should not be a problem. But, this is just my opinion about this.