I've added a patch for #1 as
ticket #993. I'd appreciate some pointers on what needs to be done for #2 (I think it is taken care of by the patch, but I'm not sure).
Also, for #3: I think it'd be possible to check that impmake exists on the path (e.g. using impmake -v) and if so, doing the html2imp conversion [or else bailing out]. For bundling, impmake depends on
eBook Publisher so that'd be required to be bundled. I feel that leaving it out of the bundle (and checking its presence at runtime) would make more sense, as unfortunately there is no native HTML -> IMP conversion (you'll need to build an almost complete HTML renderer which matches their ROM and fonts).
What do you think?