Hi Erik & welcome,

Well I guess all of us here will say go get an i30 - it's the best!! 
But I hope that your answers to the following questions may help in 
your decision.

Re: Composing...
How do you approach a new song?
If you want an instant "band" with the instruments you need playing 
in a style close to the style of your planned new song, then an arranger 
keyboard is for you (eg Korg i30 or PA80).
If you always like to "build" a song with your personal touches from 
square one, then you may not necessarily need an arranger keyboard, 
perhaps just a straight synth with sequencing capabilities (e.g Korg 
Triron, Trinity or Karma keyboard - note: the i30 also has a sequencer) 

Re: Sounds
Do you want to use any sound exactly as you can hear it (e.g on an 
audio CD)?
If so, you most likely need a sampling keyboard - i.e. one which 
enables you to input ( i.e. record) external sound samples and load 
them for playing with your keyboard (e.g. Korg Triton).
If you don't, then you could use one of several synths on the market 
but still be able to "edit" the internal keyboard sounds to your own 
liking. The difference is that you can't actuall change the internal 
sample in these syths, but you can bend the sounds and get some amazing 
results - you could take one piano internal sound and produce several 
differing pianos sounds from it (e.g. Korg N364, i30 PA80 ...). I'm not 
sure if the PA80 can actually "sample (i.e. record)" or just load 
samples from dikettes - sorry.

Re: performing
Do you want to use MIDI files?
Most synths these days will play MIDI files.
Do you want to play with full or part "band" interactive backings?
You will need an arranger keyboard for this. (Korg i30 will play MIDI 
files too)

Re: ease of use
This is a hard one and is very subjective. The more features a keyboard 
has the more one has to learn about it. Most of the current 
technology-packed keyboards are full of features. They are all daunting 
at a first glance. Do not be put off!!! I think the answer is to go 
with the technology but be very prepared to put in those essential 
hours learning the features - the key is to take it slowly and learn 
(and experiment) with one feature as fully as possible BEFORE moving 
on to the next. An good analogy is like putting someone if front of a 
PC running WINDOWS for the first time. If that person follows a tutorial 
and tries/experiments bit by bit, then they will learn effectively and 
far quicker than just diving in pressing everything just to "see what 
happens".

Good luck with your decision. If you do decide on an i30 and are lucky 
enough to find one, then remember we are all here to assist you with any 
questions (no matter how basic or advanced).

(Note: the M1 is a classic Korg flagship keyboard but is now a bit behind 
in terms of authentic sounds)

All the best

Pete