Should I use expanding foam before sealant for gaps between tiles and work surface?

No, because if it's fitted properly there shouldn't be a gap wide enough to use expanding foam.

No,between the tiles and the worktop you should use silicone to prevent water siting and eating away the grout

No most definitely not

Any gaps that large shows the installation may be incorrect, there may be movement of surfaces.ie, walls, units appliances what ever you are attempting to seal or area you have had tiled

I would advise investigating and securing the area to eliminate any or further potential movement.

Use the correct water proof grouting or fillers allow to dry for 24 hours

This ensures that the silicone has a solid and water proof foundation to sit upon allowing it to do its job properly and in accordance to the manufacturer's requirements.

It depends on what type of crack you mean, you can also use silicone, you have to see

You could use filler or foam but think filler is best to get that level look before you add sealant

Not expanding foam as some silicone can melt the foam….better with the rolls of expansion joint foam, specially developed for silicone joints….

Sean????????????