I largely agree with /u/jrochkind, given you & your staff's current level of expertise, going into a whole-sale rewrite into Ruby right now is NOT a good idea.

On the other hand, long-term a rewriting the system to be more contained & maintainable is probably a good thing. The key is to not put all your eggs into a basket you are tossing off of a waterfall.

First step is to get you & your staff more familiar with the new technology & techniques you want to transition to. That is the single biggest thing. Until you are confident you are competent writing code in Ruby (or Java, or Javascript, or Python, or <insert lang here>), DON'T do the rewrite.
You also may want to rethink moving straight to Ruby. I love Ruby to death, and it makes getting things done amazingly easy, but the language is NOT perfect, and it's problems will bear directly on what you are looking to do with it here.

Mastering Ruby requires knowledge of a lot of advanced programming concepts (eg. proper pure OO modeling, meta-programming) which can be both intimidating to newcomers, and also extremely easy for said newcomers to abuse/misuse, particularly in larger more complex projects. This was why in the early Rails days you heard folks say Rails was unsuitable for anything beyond basic CRUD apps, you had a lot of juniors and/or PHP devs jumping onto Ruby and making giant messes of spaghetti code (and Ruby lets you make some very nasty pasta).

Ruby also has several performance trade-offs endemic to it's design. It would rather make it easy to do complex stuff, and allow programmers to be flexible, than to run fast. Ruby will NEVER be on par with C/C++ or Java, and that is just the nature of the beast (this is not to say that you can't write fast code in Ruby, just that there is no way for Ruby, overall, to compete with Java, etc. in writing fast code)

If you are still looking to do the rewrite in the long term, I would strongly recommend looking at Java (first) instead. It is more performant, Makes it harder to shoot yourself in the foot, and is more familiar to PHP devs (in part because PHP has started to borrow things from Java land as they have tried to fix the many many problems with PHP). Java has it's own problems of course; but it is still a better transition option in my opinion than going whole hog into Ruby. Plus, you could always utilize JRuby and start a 2nd transition pretty easily.