Re: Skills
there are a few factors to take in as well , i myself had crew on sixth skill over two years ago and they are still on sixth skill so take that into account go for five skills per crewman as your average maximum.
the skills are not linear in the fact to get skill one is quicker than getting skill two skill three is probably the combination of skill one and two in time and battles , its just not linear.
a small crew will of course increase skills quicker than a large crew as each battle the crew takes it in turns to get the increase of points they dont all get the lot every battle.
most players will settle for three skills and not hotswap crews with prem tanks which of course will more than double the crews progress if he is fighting in two tanks and one is a prem.
I ALWAYS have my commander training as mentor even on his sixth skill its still mentor there are two methods , the gold way (pre wargaming ban days) or the skill reset way,
the gold way is simple enough have your commander on mentor , when he gets to 100% pay the gold and retrain the first skill to sixthsense , now set him back to mentor , until you reach second full skill ,change this to BIA and set him back to mentor,
depending on the tank all other crew are waiting for the commander to get his second full skill and his BIA , you then reset the crew and make sure they all get BIA and what ever else you like be it repairs or cammo with vents on the vehicle crew will be up around 120 more than enough to see any difference in performance(note here i found russians get most from crew skills ??? could just be me).
if you dont want to use gold , you need to make sure crew member or commander has enough to reset and still be above 100% in one skill , you will loose around 30% this way so train to 130% combined and reset to 100% single
of course do the crew skills make a difference ? yes they do indeed but i would argue gold consumables make as much of an impact on performance , watch leet players they play vanilla clients that look shit ,yet they all carry crates of coke and the like. bit like gold or silver ammo??? no contest ,same with gold consumables major update to your crew. and of course both cost you REAL money