For Int. Tempo I think you could get as high as 2000m to be honest. I've seen it work. You just gotta make sure form stays consistent and you're still able to run at a decent speed the whole time. Hell, if you look at programs like Baylor and UW-LX, as well as Florida, too, I think, they pride their programs on Int. Tempo a lot and I know for a fact Baylor does plenty of Int. Tempo over 2000m.
The 2nd plan you proposed looks fine, especially for just regaining fitness.
The Int. Tempo affecting other workouts goes back to CF's theory that Int. Tempo is "too fast to recover from and too slow to be used for recovery" (or something like that).