I think AVC1 is the proper FourCC for MP4, but perhaps bond just forgot to hit me over the head until now
quantizer: it's an up/down control, so use whatever values you can obtain with the up/down buttons
Unless you're telling me I screwed up the limits, all the up/downs have been adjusted to allow only entries that are permissible (though I don't know how they act if you start typing away and don't hit enter (hitting enter will enforce a valid value)). I think quant1 is the standard for best quality.. I've never heard of quant0.
You'll also have to dig through the x264 thread, where you'll find suggested useful settings. For instance, if I'm not mistaken you should not use more than 1-bframe, and 3 reference frames is already much.
Bitrate: you obviously have to calculate that on your own
Codecs generally don't provide a calculator that really holds for each output type and scenario. For instance, you'll be hard pressed to find reliable overhead values for MP4, with a fixed 1b-frame GOP structure (I think x264 GOP structure is fixed but once again I could be mistaken.. better read the x264 thread).
The fix checkbox for the buffer size is there that you can enforce a certain buffer size. By default, as long as you're in an encoding mode where you can specify a bitrate, the default buffer value is = bitrate. But on that, you'll also find some suggestions in the x264 thread.