Thanks for the suggestions!
Rondane to Hafjell is probably nice and easy route. Have gone far Venabu till Hoevringen and might very well try the Southern direction.
As for Trekanten - definitely more challenging! The problem might be the route marking in March this year - the Easter is on April 20 and we are planning the trip around March 15. Not yet ready for unmarked routes in the mountains!
Any suggestions for Hardangervidda area?