well, all the models you've mentioned here all do different things... in your list, you've got maximizers, compressors, pre amps and multi effects processors....

If you are looking at a complete OTB rig, then, with the exception of the maximizer, you'll likely need all of the above. Compressors control transients, gates (expanders) control noise, pre amps allow you to gain-up your signal to varying degrees and with varying results depending on solid state, tube, or hybrids, and multiple effects units like the Lexi will give you all kinds of choices with FX such as delays, reverbs, flangers, chorus and a variety of mixed effects...

It's impossible to tell you which to buy ....most people who still use OTB peripheral gear have multiple racks full of various processing gear and often will have doubles, triples, and even more than that of one unit when it comes to things like compressors and gates, although I'm gonna suggest here that with the exception of the dbx 166**, most of the OB gear you are looking at isn't really high quality stuff, nor is it really needed with the slew of plugs available - and at a fraction of the cost.
( ** and as far as the dbx 166 goes, it isn't really what would be considered to be of "boutique" quality either, but personally, I like them and find them worth the price)...

IMO, with the money you have and with what you are doing, with the cost and choices of plugs available, you'd be better off staying inside the box with plugs... unless you were going for something which would really add high quality coloration and high quality level of processing, for example, say a Urei 1176 or a UA LA2 (and the $300 you have to spend wouldn't come close to purchasing even one of these anyway) you are better off sticking with plugs. You'll get a lot more bang for your buck.

If you are convinced that you want peripheral gear for processing, then for the money you have to spend, unless you are looking at used, it's doubtful you can do them all. Only you can decide which you feel to be the most important element in your rack based on what it is you want to accomplish, and on that note, I guess I'd suggest the dbx, because it would at least allow you to use a real compressor on your incoming signal, and it would also allow you to strap it to your two mix output if you were mixing to another PC, tape machine, etc.

You should also consider that when using OB gear in a digital realm while mixing, if you are using aux sends to loop these effects in the classic send and return scenario, you can run into real problems with phase and latency, unless you are processing "front loaded", which means that you are running your incoming signal into the analog gear first, and then into your DAW... but that would mean that you were "printing" this processing, and that's not a good idea either, with the exception of maybe some light compression to tame transients on the way into your DAW, because then you are stuck with whatever tracks you have recorded having those effect(s) permanently there on that track, at which point, if you decide you don't like the effect, you're hosed. Once an effect is printed to a track, you can't undo it.

Stick with plugs. For what you've described as to what you are doing, you're gonna be better off, and you'll get more processing choices available to you for what you are spending.

IMHO of course.

Another cheap vs quality result question ! smoke

Assuming you went cheap on the audio interface also, I'd say don't do OTB at all... just going out and in of average converters will degrade the signal enough to discourage you from doing so. Add average gear in the middle and you may have a disaster on hand ! Just my humble opinion... you are better off with good plugins that you may already have but need to learn better and a good listening environement (good monitor and control room)

Now if you have some mytek AD and DA converters, that's another story in which you might not want to consider cheap OTB gear anyway !!!