Givin the situation you are describing, I would just go without the ears for now. If you practice with ears, then it will be pretty akward to play shows without them.
Pro's of IEM's.... Good isolation, easier to add certain effects, you can get some spacial imagry, you can get away with lower volumes (although there are studioes that show that the damage caused is about the same with or without using IEM's), drastically reduces feedback issues, easier to shape the tone, freedom of mobility without worries about hearing properly.
Cons of IEM's - Batteries, RF Interference, cost, proper fitting of ear peices (many people have problems with ears staying in without custom molds, this can prove to be very irritating and distracting), detachment from surroundings, volume (many many bands play loud enough that your budget ear systems can not keep up... this definately includes the Shure PSM200's), monitor mix is harder to assemble since now you can hear so well and demand a different level of quality, everything needs to be mic'ed in order to keep a smooth ear mix.
After working with well over 1000 bands live and at least a couple hundred bands that use IEM's, this is my experience. Go with the Shure systems, but try and save up and get
the PSM 600 or 700 unless your stage volume is fairly low, and then
the PSM 200's also become a viable option. The reason I do not reccomend
the PSM 400's is the plastic body pack that will inevitably get dropped and break. I would say that at least 90% of the bands that I have worked with that use IEM's are using Shure transmitters and receivers. Most of those bands are NOT using Shure ear peices though. Personally, the e3's seem "ok" to me, the e5's are definately a step up. I have not personally used or worked with the e4's, so I can not accurately give an impression of them. I find that most bands are using Futuresonics or Ultimate ears. Almost all of them have told me that they started with shure ear peices, but greatly prefer the Futuresonics and Ultimate Ears buds, and they often cost less as well. Many people have told me about their nightmares with things like Nady IEM's and AKG IEM's. The Sennheiser users seem to be pretty happy, but many have switched over to the Shure's for more consistency and reliability. The Sennheiser models from the last couple of years seem to do much better than they used to though, so at this point in time, I would even consider Sennheiser as an option.