Hi Paul
I think it's do-able. Firstly, great choice with the WT, I built one nine years ago and it's still my favourite. It rides beautifully, so comfortable, I also use it for commuting and general leisure riding, not fully loaded touring though without doubt it's capable. Wheels are in my opinion the most important first buy - maybe £300 for some handbuilt wheels. The groupset is more tricky, £300 for a Tiagra groupset, not the prettiest but functionally sound, but this will need some thinking of the type of riding you want to do. On mine I use a Sugino Alpina 48/34 crankset with a 12-30 cassette, but a groupset is an economical start. I love the Nitto Noodle bars, together with a stem and seat post maybe £150. You then have tyres, some small bits and then the build cost. - £1000 should be OK. Brakes are important - without doubt Paul Touring Cantis are my favourite, but at around £100 x 2 they are expensive, the Shimano cantis are the best alternative in my opinion.
Hope this helps - been a while since I've posted here but can't ignore another Bob Jackson fan!