1. You might toughen them up a little. Avoid full sun (cloudy
days are better). If they go back inside for days on end to avoid
rainy weather, you will need to do this again in the week before
1st of May. Watch out for slugs.
2.Bleach solution dip works.
3. If you have access to a nursery/greenhouse supply,
you can probably find professional container mix for
this. These are all good choices:
http://homeharvest.com/pottingmixes.htm
If not, Black Gold is a decent retail product. Granny likes
Expert Gardener Organic from Ace Hardware (works well
for her, good price).
If you want to make your own, you can mix 1/2 coir,
1/2 perlite then mix 3 parts of that to 1 part earthworm
castings. No fertilizer required. The coir soaks up water
better than peat. It gets wet faster and stays wet longer.
By volume, earthworm castings are not cheap if purchased
retail, so this is not likely to save anything compared to a
bag of high-quality container mix unless you have your
own worm bin. You just won't have to bother with the fish
emulsion or other starter fertilizer before transplanting
outside.
4. Usually not before they have 2 sets of true leaves. Fish
emulsion works better as a soil drench than as a foliar spray,
in my experience. Some professional mixes have a starter
fertilizer mixed in.