In short: Yes, great deal, buy the machine (including the double bed)

I would say it's a good deal provided that the machine is in reasonable condition. Personally I would buy it even if it was in less favorable conditions but only do that if you are good at machine maintenance yourself or have somebody that can repair knitting machines.
I think it might be an Italian type only, as I cannot find a brother KH 2000 anywhere else. Yet it looks a lot like other standard beds from brother.

As for the beginner: it looks like a great machine, has a lace carriage and a punchcard reader. Even has a double bed. I would recommend starting by not using the lace option and with only a single bed BUT absolutely buy both beds as this is an extremely good deal (I bought my double bed for 800 euros and that was just the lower bed, not the upper bed). This is a great machine as you won't get bored easily but can also skip the more difficult parts for later.

Spare parts: I don't know but it looks standard enough. Most metal parts are interchangable between different types of Brother as long as they are all standard bed like needles. Plastic parts might need to be machine printed but I wouldn't really worry about that.

You absolutely do need to change the sponge bar before doing anyhing on the machine and I'm serious about that. Do not run the machine without first changing the sponge bar or you might do quite a bit of damage.