The b Akasaka Hotel is actually quite a walk from either Aoyama Itchome or Akasaka-Mitsuke Stations (both on the Ginza Line) so I absolutely wouldn't recommend it with luggage. If you catch a taxi, no problem. In general, Akasaka is a really conveniently located neighbourhood. The b is a nice, modern hotel too (less than 10 years old). But it's located at the top of a steep hill about 10 minutes walk from Akasaka Station (it's almost the same distance to Nogizaka Station). If you have normal fitness it won't be a problem, but if you had any mobility issues, that steep hill would be a big barrier. Also, since you're in the area, check out the grave of Raiden - the greatest pre-modern Sumo wrestler behind the little temple at the base of the hill.