Generally you would want to have vents along the eaves of the roof, then vents at the peak of the roof and a clear path for the air to flow as pictured on the following web page.
So far as the knob and tube wiring, I would have it all replaced with romex if it is acceptable to cover the romex in your area with insulation, then not to worry about that.
So far as the recessed lighting, no matter what the label says, these can get *very* hot and damage/melt the insulation on the wiring. I would have the electrician verify that these are wired with appropriate new high heat rated wiring. Then I would also be sure to not cover them with any insulation so the heat can dissipate.
So far as how much insulation, with the current high energy costs, I would add as much insulation as possible to the attic and also add the roof top insulation. It will probably be worth it in the long run. I don't know what your heating and cooling costs are, but if you want to lower them, then consider the cost of this work -vs- the cost of added insulation.
And so far as spray foam around the existing electrical boxes for ceiling lighting, again these can get to be quite hot as heat travels up. I would re-wire with appropriate new high heat wiring and ask the local building inspector what is allowed. I have seen these where the heat from a regular light bulb has caused the insulation on old wiring to fall to pieces leaving bare wire (was not high heat rated wiring). Personally I would tend to want to leave a little ventilation above these just like the recessed lighting.
Overall, your area may require a building permit to install insulation. Good idea to get a permit and discuss your plans with a local building inspector before the work is done, then have it inspected after the work is done. If no permit is required, might want to see if you can pay a building inspector to check it out in their spare time or something - make suggestions as to what would be best.