I own both amps. The Mk V is my main amp and the Express Plus 5:25 is my small gig amp. I call it "mini MkV". I also have a Royal Atlantic). Here are a few observations about the two amps:
1. You can get some very good tones on the E+, and standing alone it is quite usable. However, virtually every comparable tone on the Mark V sounds better (bigger, richer, rounder, tigher, more impact, etc...) Between the circuitry, the difference in tubes, etc.. there is a reason why one is the flagship amp and the other more of an "entry level". So, while I gig occasionally with the Express, and have dialed in some good tones, if you are totally into your tone, I'd suggest you play them both and decide. I realize you said you don't care about all the features and options, but there is a difference in the quality of the tonality across the board, which may or may not be worth the money to you. Coming from playing an ED, my suspicion is that the E+ will sound small and thin to you. 5 watts, or even 25, through EL84's is a far cry from the girth and punch of the mighty ED.
2. I am not sure what kind of music you play or what your intent is for your three "tones" idea on the E+, but..... I am skeptical that you can get enough variation in your tone, or your volume, using just the graphic EQ to be satisfying. In other words, if you dial in a tone you really like on Ch2 without the GEQ, my inclination is to feel that you couldn't get a killer third tone just punching in the GEQ. You can get a different voiced tone, to be sure, but I am not confident that it would be great tone, and most of us look for great tone in our gain/lead tones, right? I think if the Hi/Lo variation on the ED wasn't enough for you, I don't think the GEQ variation on the E+ will get you where you are seeking to go.
But, that said.... I have found the the Flux Drive Mesa pedal is voiced really well for the E+. It does sound like a fantastic lead channel tone and is very organic, in that it sounds like a Mesa channel, coming through the Mesa amp. That is how I get my lead tone on the Express, my third channel, if you will. I use both the Flux Drive and the Tone Burst pedals, which give me 4 variations of gain/bost/channel options. From the clean channel, I can get a great lead tone with the FD or a clipped/blues lead tone with the TB. From the gain/crunch rhythm channel, I can punch it up to a good lead tone with the TB or over the top gain/scream with the FD.
I don't use those mesa pedals with any other amp; but with the E+, they sound like part of the amp. FYI, I have a Tim, OCD, and Fulltone Fulldrive 2 available. However, with the E+ amp, the mesa pedals sound the most natural and organic, more like they are part of the amp and not a pedal.
So, you might consider that option to save money and get your third channel.
Just some thoughts... Barely worth the $.02.
Brent