Not knowing the deceased Mason is no excuse not to attend funerals, and rearranging your schedule and commitments for a funeral shouldn't be any different than doing it for any other Masonic function. If you find out about it at the last minute and have a prior obligation, no, you can't be expected to drop everything and go. But if your lodge is doing a funeral and you can make it, you should attend. If your jurisdiction does mainly graveside services in the middle of the work day, that is a little different story, but here, most Masonic services are done at 7 p.m. during the visitation. Including travel time to and from the funeral home, a Masonic service takes about an hour of your time.
I do the chaplain part. We've done funerals for people I have sat in lodge with for 20 years, and we've done courtesy work for people we've never met. There is no different feel or effort for either. These men were Masons and deserve the last rites of a brother.
As for numbers, I've been involved in funerals that there were only 3-4 there and ones with dozens. While it looks impressive to have dozens of members come in to say goodbye to a lost member, I think the absolute best number is 11. When you have the WM, chaplain, and man holding the Bible at the casket, then four flanked on each side, it looks really crisp and balanced.