ok you get 1 character/pilot per account
there is no reason to have more
you can unlock all skills with the one pilot
so when you are max level you will be able to play scout/assault/defense/commander all at maximum capacity
you will not need to go making alt accounts or twinks
you can even level multiple trees at the same time if you wish or you can specialize early to achieve maximum power for that class before moving on
you can play scout max it out and level your commander skill with out even playing commander roles
or you can go for a jack of all trades, master of none style leveling progress if it floats your boat
you can swap modules unlock from one mech to another too, so you dont need to worry about having unused space while your leveling
go
here and read up