So I had a front suspension spring break on the van as I went over a speed bump, which went with a hell of a crunch I might add. Definitely not something I want to experience again... 

Am I right in thinking I should replace both springs at the same time? It seems logical, so that they wear evenly. Is this what a garage would do?

I did buy a pair of springs and I've replaced the broken one tonight. Everything seems okay, but on a test drive there's now a few creaking noises coming from that area. Is this usual? Is the spring just settling down and getting itself comfortable? I'm pretty sure I reassembled it all properly, and all my tools are accounted for... 

Springs should be replaced in pairs as best practice but it's not a necessity.  Most people wouldn't have both done.  

Did you change the top mount?  If not that might be past it's best and creaking now it's been disturbed.

No, I didn't change the top mount. It's a genuine FoMoCo item (the strut and spring are not so marked) and it's quite possible that it's the original item. I'll try and fit a pair of new ones, when I can face the job again. 

Springs can be a bit like Lamps, when one gets to the end of its life the one on the other side goes quickly after. I had this happen before when one broke at the bottom, the other one went before I had a spare weekend to fit the new ones.

Personally I would fit new Struts and Bearings as well, the Damper may have some damage depending on where the Spring broke.

I had mine done last October,never knew which was strange but it failed the m.o.t on it and i did ask him about the having both done and it said no,no need.

It sits A1 and level and all fine.