What to look for in a first Serger?

Hi All,
I went machine shopping yesterday ;) I'm on the hunt for a new sewing
machine (see other thread) and a serger. This will be my first ever serger.
The lady demo'd a Janome Mylock 204D for me, and I got to play with it a
little. It certainly seems a sturdy machine - 3 or 4 thread, differential,
flat and rolled hems. I found out what a looper was! Seems that it should
be reasonably easy to thread.
Is this a good machine for a first serger, and are there any other bells
and whistles I should look for? In terms of use, I want to expand my
sewing repatoire from wovens into stetch fabrics. I'm thinking about
making T-shirts and fleece tops etc, also to use the serger to get a
professional finish on my woven fabrics for the seam finishes.
Are there any other machines I should have a look at? Budget is an issue,
but I want to get a good solid machine that will last me a while. And what
about extra feet? The lady demo'd the gathering foot and it looked useful
to have - any others?
Can anyone in the UK explain how the warranty would work? This shop said
the warranty was with the dealer, and they would not do warranty work on a
machine bought elsewhere. Although I expect they would service it for a
fee.
Price - now this dealer had the Janome Mylock 204D at £249, and I know I
can pick it up at £219 from another dealer, and at £199 from an internet
store. What Dealer A is offering is unlimited free advise and help at the
store for as long as I have the machine - pretty good - these people did
spend over 2hrs with me yesterday demoing machines and letting me use
them. I do need to go and check what Dealer B is offering however.
Dealer A has indicated there would be a discount for me buying a sewing
machine and serger simultaneously, but did not say how much. From what she
said, I think there is scope for manouvre ;) Dealer A's boss should be
ringing me next week to indicate the discount.
Thanks in advance for any advice and comments.
Sarah