I use weight of eggs and same in butter ( or stork) , sr flour,sugar , and teasp of bicarb , then vanilla ess. cream butter and sugar then slowly add eggs , then fold in flour. Butter cream : 250g icing sugar ( sifted) , 80 g butter and then a couple of teaspoons of milk and beat and beat and beat .
Fondant ice your cakes when they are frozen. As they defrost, they may feel a bit damp on top but will be fine. My mum used to do lots of sugarcraft in the 90s and always decorated from frozen, it's the best way to put enough pressure on a cake to get the fondant glass smooth.
leave the cake to stand for a bit before icing - probably a bit too fresh so it splits. or put it in the fridge or freezer to harden a bit before icing. Then when you buttercream / crumb coat again fridge before putting the fondant on.