Matt,
OK...looks like you mean nebulae, rather than "planetary" nebulae. The latter apart from a couple of very large exceptions, tend to be well under an arc minute in size = really big scope to image well
My three rules of imaging gear would be "mounting, mounting, mounting"
If you can afford a high precision brand, eg Losmandy Bisque, Taka, AP. it is money well spent, as you'll be able to put any OTA you like on them later.
OTA's.....don't get hung up on aperture with CCD's. They are linear devices. All you need is more exposure time to get more signal.
There is at least one nutter out there who exposed NGC5128 for 19 hours
A high quality APO triplet in the 100 to 150mm range will do what you ask.