best rule of thumb is denoise before compression. It helps mpeg4 alot! so does desaturation of bright primary colors! keeps the bleeding down too as a bonus!
there’s some codecs like flv that can encode 12 fps and then playback 24fps. They interpolate in realtime. It’s like 10x smaller.
Also, resolution vs bitrate, google that because there really is a sweetspot called bits/pixel.\
Research what settings/codecs the professional sites use. There’s embedded divx, VP9, and even soon sometime down the road h.265 will replace h.264.
h.264 is the most popular, profiled as mkv is a stripped down version that doesn’t need all the metadata, saves a little space.
You can have multiple streams of flash that auto detect the bandwidth. Also, Microsoft Silverlight works similar to netflix, if you want to go the microsoft route. There’s tons of options, depending on your clients’ needs.