Sours are pretty easy. However, you do need patience. Just use good sanitation procedures and make sure the airlock stays full.
Keep OG less than 1.055, and IBUs below 10 and you should not have any problem. Above these numbers, you can have problems.
There is no reason for a complex grain bill. Lambics have no speciality malts, Flanders (like Le Roja) have some Special B. The bugs do all the work. This is way to simplistic, but is a good place to start for your first beer.
Extracts make decent Sours.
Either get a specific Lambic/Sour blend of yeast, or brew as normal, and toss the dregs from several commercial beers in (or both). Leave a year and taste.