As for A,B,C Q's I will go for Spouse visa A, easy for immigration as She/he spouse already B, less cost she can go work once she landed in UK and just about 2 years for ILR, unlike for fiancce visa need to marry in 6 months and had to apply for FLR again then ILR,(twice cost) C, a I said easy passing in immigration

At the end of the day, its your decision both of you, We are just giving you some idea