How big are your lettuces and how cold is it outdoors? I don't bother to pot lettuces on at all. They can be hardened off just by putting the modules outside each day for a week or so and then leaving them out overnight if it is not too cold. I then transplant them into the ground. They can be anything from four true leaves to quite sturdy little plants but they still take fine. If some of them are slightly held back it doesn't matter since you don't want all your lettuces ready at once. I do this on purpose to keep a supply coming. The leeks could be hardened off and planted if they're big enough. I can't advise on the brassicas because obviously your climate must be different from mine. I haven't even sown mine yet. They'll be sown in May, transplanted in June/July and crop throughout the winter. I'm not sanguine about transplanting arugula because it is a fast growing annual which may well bolt if transplanted. I'd direct sow it. Has it worked for you before? The kohlrabi worries me a bit too as root veg are often upset by transplanting and might also bolt.

Steve, there's no point in potting them up a few hours before putting the plants outside. The reason to move to larger pots is so they can fill it out with their roots while growing to a larger size. That takes a few weeks, not a few hours. Why don't you harden them off for the next week after you get back from your trip by just leaving them outdoors during the day? That will help acclimate them and give the garden soil a chance to dry out a little bit while you wait. Use the weekend to gradually increase their daily outdoors time. If you do build the cold frame, leave the roof off.

Don't know about the other seeds, but I have sown lettuce,beans and arugula (rocket) outdoors anytime March 31 on with success. I have read several sources that say not to plant anything fragile (like tomatoes) until after May 15. That's the last frost date around here.

Oh dear! Hope the aloes make it. I totally understand the Egyptian methods for dealing with heavy objects. We have a massive 500+ pound native limestone rock in our patio that hubby got off of a trailer and into it's place using conduit as rollers for easing it in. He's a smallish man, maybe 150 pounds. It took 4 adults to get it onto that trailer.