Yes, it's Loewenhardt
First of all, welcome to the forum!
The photo to which you refer does indeed show Loewenhardt. It was issued as part of the famous Sanke postcard series of portraits of famous aces, No. 814.
Loewenhardt and his aircraft have always been something of a mystery. Ironically for the 3rd highest scoring German ace, there are very few photos of his aircraft indeed. Personally, I choose to believe Heinz Nowarra's statement that the OAW-built Albatros D.III marked with the white snake line on fuselage and top wing was Loewenhardt's. Nowarra interviewed at least two Jasta 10 mechanics, and one of them apparently identified that Albatros as such.
Sadly, though there are plenty of verbal accounts mentioning Loewenhardt's "bright yellow" Fokker D.VII, no photo showing these markings has yet surfaced. Most likely, his D.VIIs bore yellow fuselage, struts, wheel covers and horizontal tail surfaces - but the wings probably remained in standard lozenge camouflage. I'd give a lot to see a photo of one of his Pfalz D.IIIs, too.
As for that mystifying triplane: the problem is, Jasta 10 was the only Jasta in JG I that was never fully equipped with the Dr.I. The poor Jasta 10 pilots had to persevere with their outdated Albatros D.V/Va and Pfalz D.III/IIIa types. Consequently this was the first Jasta in JG I to receive the Fokker D.VII in late April/May '18. However, it seems some Jasta 10 pilots may have occasionally borrowed a triplane from one of the other units in JG I, perhaps for special missions. For instance, on 24 March 1918, Ltn. Keseling of Jasta 10 was brought down and captured in a Jasta 11 Fokker Dr.I, 147/17. It's possible that Loewenhardt, as Jasta commander and the top gun in Jasta 10 at the time, may have rated a personal Dr.I, but there's no documentary proof of that. There's an intriguing photo in Ed Ferko's book "Richthofen", from Albatros productions, which shows a Fokker Dr.I on the same field as a couple of Jasta 10 Pfalz D.IIIa machines. Ed felt that this might have been a Jasta 10 Dr.I, perhaps even the Dr.I photographed with Loewenhardt, but there's no proof of that. It's a rear three-quarter view that appears to show factory finish only, though Ed said that the top decking of the fuselage seemed to have been painted a dark color.
So I'm sorry, but IMHO there's no easy answer to your question. Loewenhardt simply may have been posing in front of a convenient backdrop of an anonymous Dr.I, or it might have been "his" aircraft.I think your model sounds like a reasonable theoretical depiction, and sounds cool besides!!
Very best regards,