".........b. sow extremely thinly - its such a pain when they all come up
and go leggy in the fight for space and are impossible to separate.......3

This can also be caused by lack of strong enough light, the heat too great
for the type of plant...

The best way to learn is by trial and error.
you learn more from making mistakes than you ever learn by doing things
correctly the first time.
Every person finds different problems with gardening and every garden has
it's own peculiarities, just as the weather is always changing and you have
to make your own decisions when to do things, sometimes you will get it
right and other times you will be wrong.
You ask when to move your plants out into a cold greenhouse........Who knows
Depends on the temp. you are growing them in now, the day temp, and the
amount of sunshine you are getting every day, the night temperatures etc
etc.
If you cover them at night with horticultural fleece or a few sheets of news
paper then you will keep them a little warmer on a cold night... but it is
like asking how many lengths can I cut from a ball of string
Good luck.
Have you thought of joining a local gardening club?

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk