you would rather remove the brick and sheathing than go into the interior walls? What are the interior walls made of?
I would think that exterior wall holes for insulation require going through too many components in order to get the stuff in the walls and you will have to remove too many brick.
For walls, I would not recommend cellose because of its fast settling. Cellose is fire retardant but not proof. Cellose would then get around inside wall electrical boxes and could cause a problem.
Cellose clearly states on the packaging, do not get close to "can lighting in the attic area". In this old of a home, I would not want cellose around or near any electrical junction boxes.
Now, I do not know your budget restraints for this project, but I have another option for you to consider.
On, this old house, I saw a new type of wall insullation system that requires only a hole the size of a half dollar and is located at the meeting of the ceiling and wall. Of course, this hole must be between each wall stud which could be 16 OC or 24 OC, just depends. The down side is that there could be thousands of holes.
Anyway, foam insulation is pumped into the walls in a liquid state and goes to the bottom and fills up to the top. Its almost like that crazy stuff that is sold in an aresol can. Now, before you get nervous, this new stuff has no pressure buildup inside the walls. somehow they made it where it conforms to the inner walls and then dries to that size, no excessive pressure on walls.
This could be an option and I would check into it.
Remember, the walls are not just one open area, you have the studs going vertically, you must get insulation between each stud area.
You do have quite a project ahead of you. I would look at your utility bills and the cost of either project and see how many years it would pay off in cheaper utility bills and then decide if this is the thing to do. How long do you plan to live in this home? Conside that also.