Just to echo everyone's comments:
Spray malt - depends how much body you like in your beer, versus how strong you want it. A simple way of thinking about it is like this - malt has some "stuff that makes beer malty, gives it body" and some "stuff that gets completely turned to alcohol". Sugar is JUST "stuff that gets completely turned to alcohol".
So if you used all sugar, it would get completely turned to alcohol so you'd get a strong beer (i.e. lots of alcohol) but not much body - this comes across like it's been watered down, or a bit thin.
Likewise if you used all spraymalt, some would get turned to alcohol but there's also the bits that don't get turned to alcohol (we call them 'unfermentables'), which add body to the beer. So the outcome would be a beer with slightly less ABV but more taste, body, and mouthfeel.
Now most people on here are (rightly!) people who drink beer for the taste of beer, as opposed to just a way of getting pi$$ed (if we were just about that we'd all be supping cheap-o carling from the supermarket!), so you'll see (like the previous replies) that most people would recommend going the full whack with the malt - 1kg in your case. Bit more expensive, and a slightly lower ABV on the beer, but this just means that you can savour more of it in a session! Many strong beers that also have a lot of malty flavour would use, as an example, a lot of malt (to get the body up) PLUS some sugar (to boost the alcohol).
So I think that's a long winded way of saying, use 1kg spray malt
Fermentation time - Ditch is right, rack it to a keg or to bottles after about 10 days (as long as it's finished fermenting, evidenced by consistent hydrometer readings over a couple of days). It will continue maturing in the keg - there's still enough yeast in suspension in the beer for it to clean up all the nasties and generate some fizz. The reason we don't tend to leave the beer in the primary FV for too long is that the trub (the gunky stuff you get at the bottom of the FV) contains both live and dead yeast cells. The dead yeast cells can have a detrimental effect on flavour, so move it off the dead yeast and it can continue conditioning like this.
I tend to leave it in primary for 10 days or so too, then rack off to keg, then leave for as long as I can hold out. In general as long as your sanitation is good and you have an airtight seal, the longer you manage to leave it, the better (generally) the beer will be. At least four weeks if you can stand to wait that long - the kits tend to say just leave for a week or so but that's just to satisfy the punters who want cheap beer quickly.
Priming - all the different substances you've mentioned will impart a very slightly different flavour - again, pure sugar imparts a neutral flavour as it *all* gets turned to fizz and alcohol, malt will add a bit of a malty flavour as well as some fizz and a tiny bit of alcohol (for the reason above), honey, maple syrup, etc will do the same (enough sugar for the yeast to generate some CO2 fizz, but also a little bit left over to flavour the beer a tiny bit). If you're bottling, how about trying a few bottles with each priming agent - then you can compare the difference each makes.
G'luck with it!
Ten days is plenty of time in the FV, Roy. But, then ye'd really want it out of there and into ye keg / bottles. I've left beer two weeks in the FV, out of a necessity of the moment. But, it was a bit nervy!
