At this point if you want to be at all professional with your video work it sounds like you need to do some more technical reading on bitrates / file formats / file containers. I would first of all suggest NOT downsizing, as one of the whole advantages of your camera is the resolution it records in.
Adobe CS5.5 is miles ahead of FCP for DSLR video editing. It (Premiere) will use the video card in your computer to real time render most of the footage (assuming your comp is fast enough). With FCP you have to first convert your footage into something like ProRess 422, or render constantly. CS 5.5 is native to most codecs now.... and it also integrates extremely well with after effects.
In addition, Id strongly suggest taking any current photoshop/lightroom knowledge you have now and start translating that to After Effects. Just like your photos, color grading and whatnot will make a big difference on how your clients view the quality of your footage.
You can get a trial of CS 5.5 for 30 days, and youll have a lot easier time manually setting encoder settings (of which compressor doesnt even give you much choice over). The best solution, however, would probably be to use an intemediate codec and then convert your final film to H264 with something like avidemux, where you will have complete control over the codec.
In short: Up the bitrate to something like 3-8k, keep it higher resolution, and just upload to vimeo/youtube or your own filehost. 150 megs is nothing these days - theres no reason to try to crappify your footage by making it email size
edit: This page explains everything in detail about h264 encoding:http://avidemux.org/admWiki/doku.php?id=tutorial:h.264