Now for my personal opinions... :-)
I love Mac over a PC for music. It "just works" - the majority of the time. It's more expensive inside the walled Apple garden - BUT - I don't have many issues ever with them. They are computers so yes they do have problems now and then.
PC? I'm a data analyst / programmer / anything that plugs in with blinky lights person in a 2 person IT dept. I have a Win8 laptop at home. I frequently use four letter words with PC's.
If you love tinkering with PC's and updating them - then by all means - do it. If you like Mac better - by all means - go that route. You seem to be leaning that direction.
Mac's come with Garageband -before you spring for Logic - record in Garageband - it covers all the bases. This will offset the cost of the mac over a pc.
Midi Controller - seriously tons of them out there. If you can go try them. That is getting ridiculously hard these days as music stores aren't plentiful. Read up on them - read reviews.
Loren Nerell just bought a Nektar and I have to say - I've been looking at Nektar's for a long time as well. But I don't really use softsynths so ... not high on my list.
I've seen people happy as pie with akai, native instruments, behringer... I don't own one.
AU vs. VST - sheesh... get what works well for your system and you'll be fine. I did some quick google searching and found tons to argue against VST (mainly a ton of poorly made ones - which you'll get with ANY software)
You may not need many VST's or AU's or ? for a long time to come anyway. Remember - start small - explore what you have. Add when you're ready.
My recording style... software:
I'm a hardware guy. I started on piano at 5 back in 1975... so I hit my prime teen years right into the poly synth explosion of the 80's and then digital craziness. I still have synths and effects from the mid-late 80's. I hate selling. I'd rather have something I've known and loved for a decade or three than constantly sell / buy. That's me. That's not everyone.
I prefer recording audio like to tape. That's how I learned on 4-track cassette tape - and that's how I prefer to work. So when all my pc's died in the mid-00's - I switched to Mac and Logic. Logic works nicely although I still find it less intuitive than Vegas 2.0 I was used to. Now Vegas went all video after 2.0 so... it's weird.
So I record audio to Logic and occasionally I use softsynths now since I bought an 88 key piano controller.
I'm sort of in love with playing guitar these days althoguh I can't play it and my gear lust is generally toward guitar pedals. But I have 3 synths, a modular, and a nice array of hardware effects. (remember, I don't usually sell anything. :-)
Sincere good luck - and ask us anything.