"How necessary is this & does it lengthen case life, or other beneficial stuff?"
Don't think inside neck lube adds a thing to case life but it does improve the necks. Conventional expanders, by pulling from inside the case tend to stretch the thin side of a neck more than the thick side and that pulls the neck out of line with the case. Not good for accuracy and the .35 can be astonishingly accurate with good ammo!
Actually, I was happy to see that you are getting a Lyman M die. A universal decapper and the M is THE answer for best necks with bottle necks, on average and with common reloading tools. After sizing but before expanding, just rub a "greasy" (lightly lubed) finger over the mouth of the case. That will leave a slight ring of lube just inside the mouth and it will be pushed into the neck as the expander enters, viola, lubing is done! I feel that mica and graphite are half as effective.
If you lube with a wax you won't need to remove the residue unless it's excessive. I use Imperial Die Wax but if you don't have easy access to that you can also use Kiwi "Mink Oil" boot treatment, actually it's a high quality soft wax very much like Imperial and works just as well. Walmart has it in their shoe department for cheap. Wax case lube is clean, won't contaminate powder or primers, easy to apply with fingers, easy to wipe off and won't attract dirt. Great stuff!
The Remington 200 gr. RN is MADE for the .35 Rem and gives ideal performance. Nothing else I've tried does as well. Well okay, the Hornady 200 RN shoots as well but doesn't expand as well at .35 velocities.
