1. Not directly, most chasecam mods should work fine, just don't hack the view angles.
Alternatively you can implement a chasecam via csqc, but its more involved and there's no examples around.
I've never been keen on the idea of adding a chasecam directly into the engine as a) it breaks mods that already have chasecams. b) it can be used to see around corners or through walls in extreeme cases.
2. there's a pr_dumpplatform console command which will write out a file. Said file contains lots of builtins and things that you can link against. Its basically the equivelent of dpextensions.qc but doesn't have many... well, any... comments.
for features that are mutually supported by both fte and dp, you can just peek at the comments in dpextensions.qc to get an idea of the extension.
Or you can poke me on irc.
3a. HLMDLs have not been tested for quite some time...
With csqc and the base* and bonecontrol* fields (see pr_dumpplatform), you should be able to get animations that match those seen in halflife - separate leg/torso animations coupled with waist twisting and mouth control. What there isn't any support for is obtaining waveform information from audio files for lip syncing, but you should be able to get some mouthing working.
3b. Q3BSP objects rotate around origin brushes. Shove in an origin brush to define the object's origin and it'll rotate around that by just setting .avelocity.
Q3 shaders should generally work, although you can get extra fun stuff from creating glsl programs to go with your shaders - there's a r_dumpshaders command to dump out the built in shaders, and some distort.pk3 file on the svn that serves as an example of how to invoke it ('program foo' directive inside the shader, gives some weird distort effect for explosions).