If you can afford the $$, get an HD500x. Just because you don't intend to use every one of the FX on the HD500, doesn't make it any less of an excellent tone machine.
A couple of thoughts for you to consider:
- Line6Link: when using an HD500 or 500x with the DT, you can connect them using the L6link feature. This is utilizing the preamp portions of the HD amp models, while using the DT to provide the rest of the signal. It configures the DT amp to run in "combo" or "stack" mode, depending on the type of DT. In your case, "Stack/poweramp". This option disable the mic and room modeling from the HD500; however the XLR out on the DT adds cabinet modeling back in ,so that signal sounds appropriate for recording and sending to the PA, monitors, etc.
- "Offline" tone creation: when not using the DT amp, you can still dial in your patches and FX routing, utilizing the HD500 in 'studio direct' mode at home / studio, etc., and use it for direct recording, or direct monitoring to any available speaker. There may be gig situations where bringing the DT is not feasible, and being able to bring just the HD500x will enable you "your sound" in a portable form. I personally build my patches with *very* sparse use of the FX. Compressor, Drive, Reverb, and Delay. Sometimes I will add a second reverb and set the footswitch to toggle between two reverbs, usually a light, subtle spring 'verb, and something more spacious, for effect.
-JTV guitar: if you ever decide to get on the Variax train, the HD500 is a very useful item to have for pairing with the JTV. All additional control features aside, the HD500x powers the JTV, which is a good thing. Beyond that, you can do a whole ton of cool things with an HD500x, in terms of how the JTV interacts with the HD500, like, set certain FX parameters to be controlled by the tone knob on the JTV. Like drive, gain, delay settings, etc.
It may seem like overkill, when you intend to only use a few pedals. As far as the non-HD500 pedal route, I definitely love the simplicity of one or two good pedals. Keeley is my all time favorite pedal designer. That being said, since you already have the beginnings of the 'dream rig', at least take some time to read up and if possible, plug in and listen, to what the DT and HD do when paired.
One last thing, the most recent DT firmware update does allow you access all the HD amp models on the DT - I am not sure about the specifics of how that works, I think you still are limited to the # of channels hardwired on the DT, but I think you can now assign any of the HD models to any of the settings on the DT, replacing the 'stock' four or eight or whatever it comes with. I use an HD500 with my DT25 1x12 combo, and so I never actually did the DT firmware update. I think you need a MIDI interface to update the DT firmware, it doesn't use the standard USB to L6 Monkey type connection.
That's my two cents! I just look at in terms of, two or three good analog pedals will cost more than one HD500x, new. I mean, a Keeley 4-knob comp is around $250. A Keeley Time Machine is $290. To get a decent collection of volume pedal, wah, compressor, noise gate, distortion pedal, reverb pedal,chorus pedal and delay pedal, you could easily spend $2,000-$3,000.
While it may not *seem* now like you need all those pedals, that is really just the tip of the iceberg for many people, in terms of 'stock' effects.
Why I like the HD500 route so to speak, is you don't have to use ALL of these FX at once. You program your favorite amp models, and you dial in FX blocks that you like, and create a handful of good patches, using FX where needed. I just like to know, that if I need them, any of the M-Class (M9, M13) series FX are available without any added cabling or pedal power needed.
And since most external pedals run in series, when the one in the middle of your signal chain goes out, the whole pedal train stops working.
But that's just my opinion! I actually feel pretty at home programming patches, and using 'digital' FX. I did it backwards from you; I bought my HD500 in 2010, the DT25 in 2014. By then, I had gotten accustomed to programming the HD500, using it with a variety of amps and monitors, speakers, PA's, keyboard amps, etc. Plus used it ALOT at home for recording.
So for me, the DT was a natural extension of the rig I was already at home with. So I can why you are looking at it as, do you really need the HD500, or will the DT with some pedals do the trick? That's why I suggested plugging an HD500x into your DT rig, and see what the L6Link does for your sound, see if you like it, and how it works.
Cheers! Best of luck to ya finding the right fit for your rig