It is really a bit early to plant out courgettes: cold nights will see them off, and we can't really guarantee frost-free nights until June. You may be OK, but they don't like the cold.
I use copper rings to keep slugs at bay on individual plants until they are large enough to manage on their own, but this is an expensive option. You can also try coffee grounds, ground up eggshells or purchase wool pellets at a garden centre (they swell up to a sort of felt).
If you go down the slug pellet route, use the environmentally more friendly ferric sulphate ones rather than metaldehyde - and don't use too many, a very thin scattering is adequate. You can catch slugs in beer traps ... yoghurt pots sunk to within 1/2 inch of the rim, with an inch or so of beer in the bottom.
The peppers and tomatoes will both be very much happier growing in your greenhouse than outside. Both need warmth, and indoors the tomatoes will have thinner skins and won't get blight.
Sow the peas outside now. Broad beans can also be sown outside now, although it is a bit late. French and runner beans can be sown now, but I would sow them in pots in the greenhouse for planting out after all risk of frost is over.
Good luck! Slugs are a sad but inevitable part of gardening life, I am afraid.