Assuming your 'other things' are as 'normal' for this country as marigolds and sweet peas, then you shouldn't have any really critical temperatures to worry about Pam. The shed is probably a no-no if you want early germination and even the garage wouldn't get seeds to wake up yet. I think the spare room looks fine for most things but if you decide to go for tomatoes or chillies then they would need a bit more and the kichen is a far better choice. I usually have a kitchen full of toms etc. soon after Christmas and believe me it is a nuisance trying to work when you can't move. Lol. The other beauty of the spare room is that if you should neglect watering for a couple of days, the pots, trays won't dry out so quickly. Quite an important point if you have a memory like mine. So I'd go for the spare room for border and bed type flowers.

I would also prefer the north facing window sill, Pam. One problem with a south facing window sill is that when the sun shines (yes, it does sometimes) it can get localy hot behind the glass and tender seedlings can be scorched.

Thank you both. I'll be setting up an old bookshelf to hold the propagators in the spare room then :)

The other things will be vegetable.