One of the biggest differences between the LD and Sennheiser, audio aside, is the RF section. The LD has fixed channels. If you are planning on running a lot of wireless, you are going to be running into intermod and interference problems pretty quickly if you can't fine tune your systems. Yes, you can choose a number of channels if you are using the same gear, (e.g. IEMs) but if you start throwing in Mics... and even add the complexity of different manufacturers, you're going to run into problems pretty quickly.
UE900s - defo, they are a bargain under 200 - the eglobal link has been bounded about a bit previously. I wouldn't be looking to buy them for anywhere near the rrp!