Hi
looks like you are on the right track, but just to share some of my hardships you might want to avoid when tagging classical music ..... Now if you search the forum you will find lots of posts on this, and there is no standardized way of tagging.
However, the more your collection grows, especially when you have more than one recording of the same works, good metadata, once its there can be re-manipulated as you go ...
one thing to remember as was already pointed out to you, is that JRiver bundles albums using the Album Artist and Album fields. Although there are workarounds, you don't want to mess with this too much, especially if you have boxed 17cd box sets of Mahler etc.
Your choice of how detailed you want/need to be is up to you of course. But most classical collection are indeed based on Composer. I recommend duplicating the composer in the Album Artist field -- I know it seems redundant, your views will still be based on composer, no worries there, however the album will always stay grouped together, regardless if your main filter/sort is by your "interpret" field or any other way of filtering
I also double up my Orchestra field which becomes fills in the Artist Field. The conductors last name becomes part of the album name in brackets. I also use the Period, Genre, and Style Fields as well as Soloists [for info/ you might want to use the Soloist field rather than create a field "interpret" -- this is a standard vorbis comment field and write to file as PERFORMER. Some external taggers and databases use this which could be very handy in the future. I also have created a new field called Work, and some here on the forum create again another field called Opus (my classical collection is not big enough to warrant this yet, so I combine it in Work for later).
Regardless the key is to be consistent, and Album Artist = Composer is really something to think about before you plunge into hours of retagging.
AS I'm lazy and probably boring you with the detail anyways, here's a screen shot from the new tag window to illustrate what I do. Of course, you do NOT have to do it this way
The soloists could of course be the principal piano player of a concerto for example, but some might put him in the artist field ... just a question of choice and consistency, once again.