Personally I'd have waited for another couple of months and put then straight into the garden where I wanted them to grow. I've never tried replanting onion sets from modules.

I started mine off in modules last year but didn't start until April. They absolutely romped away and were lovely to plant out.

A frost free porch would be good and yes, water when needed.

I'm of the same opinion as MG, I would have said there is little to be gained by planting in modules. I would say that they would grow away quite quickly planted direct without any check in growth. The only other thing you could do would to place cloches over the planting bed and plant below when it becomes a little warmer.

My experience of 'early start' planting methods is that they involve a lot of work and care with the resultant vegetables only being a few days earlier than than those planted conventionally.

Thanks everyone, will see how they go :-0