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Omoh, this na better question wey persin dey suppose think everyday, make I talk in my own little understand, to me ehh, mining require steady electricity, and as such, the mining equipments too dey expensive no be chaise. The answers to your questions be like this,
Ans 1, yes, it's profitable to mine bitcoin if only your equipment is updo to date an fully functional, beside, accepting tx to next block is competitive among miners, If your mining equipments are intact without obstructions, mining in Nigeria would surely be profitable.
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?
Ans, 3: Me I no go fit tell you say them dey sell mining hardwares for here or there in Nigeria, AFAIK, the only place them dey sell this things na Amazon, na them get am plenty and beside, e too cost even our 1 year signature money no go fit buy one hardware.
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.
Ans 5: Financial Factor, Regional factor, and others.
I no too ideas about Mining, so accept my little input.