I recommend staying with one "main ride" at 1st such as a
spit 5 or 9 its a well balanced plane for all dogfighting use, its very forgiving to mistakes you will make at first.
a a6m or nik would be my choice for a turn fighter
La7 , 190d ,F6F ,any 109e /g, and P 51 for a Bnz fighter and learning throttle control /energy tactics
the mossie,bf110,and p 38 are all great handling twins use bnz tactics with them.
I myself started in the F4u and stuck with it dying repeatly til i mastered it . then i went into a spitfire.I became a ace overnight in a spit.
i think my learning curve was twice as long as anyone elses because i picked one of the hardest planes to master in the game.
So pick one plane and learn it well and try all the others at times to start getting the feel for their differences . But always go back to your main ride when you get discuraged /or just having a bad day.
To get better at ACM start having duels and filming do alot of 1 vs 1 work .
Im sorry I cant recommend the P51 as a great "starter plane because it isnt,
it take alot of practice to master a p 51 to its full potental .( i see more p 51's cartwheeling in the air then any ther plane )
my best advice it to try to avoid head ons and learn to out manuver your opponent. extend and run away when you lose the advantage .