There are many challenges in modern electronic production. A few of it are related to RoHS components. Some may be unexpected at first sight.
My personal experience is that most problems are well understood and managed by designers, procuction managers and assembly houses after more than 10 years.
1. I'm not aware of Pb-free specific changes in component footprints. Selection of stencil gauge and possible aperture variation is mostly a matter of component population on a specific PCB and should be always discussed with the assembly house.
3. Some old components didn't tolerate Pb-free solder temperatures, a very few may be still in use. Datasheets and manufacturer application notes should tell. There's an absolute incompatibility of BGA components. Pb-free BGA balls must be soldered with Pb-free paste, SnPb balls with SnPb paste.
5. Just an example of unexpected. Pb-free solder at respective temperatures has an increased ability to dissolve copper, e.g. very thin wires or via throughplating. Beware of excessive solder times e.g. with hand solder.