You bring up some good points here. I would suggest buying a 50 or 35mm lens with an f-stop of 1.4 to 1.8 instead of an 85mm lens. The reason for this is due to the crop factor of the T4i. The T4i has a crop factor of 1.6x meaning that an 85mm lens will end up looking like a 100mm lens due to the size of the sensor. As such, it seems wise to have a much smaller mm lens in order to get both wide shots and close ups during a shoot. A 35mm lens will end up looking like a 45mm lens on the T4i which should be perfect for wide shots and glamour shots (since 50mm is the equivalent of what you see with your eye and it doesn't bend the image at the corners).
Also, I think it is wise to get a lens with as low of an f-stop as you can afford. You can never have a lens with too low of an f-stop. Just remember you can always close the iris/aperture if the background looks too creamy or out of focus! However, I'm sure you'll fall in love with the shallow and professional look of f/1.4.
Here's a couple of lens options that I would suggest and can vouch for having used them on many professional productions:
1. Canon 50mm f/1.4 ($349): http://www.bhphotovideo.com/c/product/12140-USA/Canon_2515A003_50mm_f_1_4_USM_Autofocus.html This lens not only gives you the ability to get wider shots, but it does so at a great price. However, there is no Optical Image Stabilizer on this lens for steadier video. For that, you'd have to buy this Canon 35mm F/1.4 USM lens for a much heftier $1329: http://www.amazon.com/Canon-35mm-1-4L-Angle-Cameras/dp/B00009R6WY/ref=pd_rhf_dp_p_t_2_B657. However, if you'll be shooting on a tripod, the Optical Image Stabilization will be unnecessary and will allow you to save a lot of money in the process!
2. Rokinon 35mm f/1.4 ($431.95): http://www.amazon.com/Rokinon-35mm-Lens-Canon-Cameras/dp/B004X1SG12. Though this is an off-brand lens, my experience with it has been rock solid. Again, you don't get Optical Image Stabilization, but you do get a very shallow depth of field, a good build quality, and a solid iris and focus ring.
Good luck with your filming and have a happy 4th of July!