Hey huntsman,
Being from Melbourne, I have a pretty similar weather pattern to you, although I think you get an earlier spring than I do (it only just hit 20C for the first time since winter on the weekend).
I started my plants very early this year, I think June 1 was the first time I planted a seed. This was great, but boy did I run out of room pretty quickly.
Putting plants outside to gradually get used to the sun is great, but if you haven't got any sun, you get into a situation where your plant growth actually retards, and the plant gets sick real quick. I think I need to invest in a decent greenhouse because the crappy $25 stuff I got from a major discount store here really sucked balls.
On the weekend, I managed to put some plants outside for the first time, and you can see really quickly that they suffer with the massive UV difference than what they get under artificial lights. But if you can put it in such a way that they get a few hours of sun followed by some shade, you'll find they will adjust within a few days or so. Don't leave it too late into Spring, because the leaves can burn pretty quickly but they should be alright in the low 20's.