The issue is, T-Mobile & Metro PCS will be using the 1700 frequency band, at least part of the time still, AFAIK. The Verizon S4 version lacks that band, hence you have gimped devices on your hands.
That said however, T-Mob has re-farmed some areas for 1900 service, and added LTE, so you may have some luck there. Whether or not that applies to your situation/location it's hard to say w/o much research/testing. I suggest you also post your questions @ howardforums.com, one of the better sites to help with this type of thing, or at least get very granular level feedback from real users, some in your actual area. Lots of <vocal> Jersey folks on Hofo, luckily. Personally, I would be hard pressed to use T-Mo w/o having 1700 under the hood, especially if under contract, and using a non-carrier supported model. YMMV, of course.
<stepping onto the soapbox>
You should have asked about porting the corporate number/discount before worrying about the phones/service. Most sales situations/discounts are not necessarily set up/based on any sort of transferred corporate discounts, as many are often grandfathered.
FWIW, you corp arrangement seems a bit odd, at least how described. Normally you see a percentage discount off the primary line only and also sometimes that line's data plan, or the shared data plan. Weren't they willing to knock off 15-20% off the primary line too when you port?