Nigeria are always really easy to manage internationally-they take anyone at any level. Was yo-yoing between the CHampionship and League 1 whilst winning the World Cup with Nigeria!
If i remember correctly the problem wasnt platform specific as its down to the third party authentication system rather than soemthnig in the game. When you load it just choose to authenticate via Uniloc rather than Steam. Thats the bottom line.
If i were you i wouldnt bother using Steam. I installed, registered via Uniloc and then downloaded the patch from the USA mirror in all of about 15 minutes rather than 15 days.
there are some useful links on the FM Forums for checking your prudoct key but other than that I would buy the CD...
Also if you try and sign a player for a fee above what you have, you can adjust the budget and reduce wage budget and increase transfer budget. I managed to get 300k for players.