NPC: Guild Master is asked who could lead this mission
Player: Take X NPC to X location option to meet them there or send X NPC with them and met them there. (You would have the option of joining them or sending member's on that mission later to find out the outcome within 48-72 hours game time) Doesn't always have to be group missions. It could be single jobs. But what determines the outcome is equipment available in the Guild at that time either through NPC sent quest commanded by you or you finding equipment in the game world to bring to the Guild's chest which NPC would take and you would later see them wearing. Training would also be allocated from the player to each NPC and each has a limitation. All this without being tedious in management.
As time goes by you would later find out the outcome of that mission based on the decisions you made and who you associated within the guild figuring out there strong and weak points. Send someone in that doesn't know to much about that particular situation the mission outcome has a less likely success rate. The member would either be killed off and your trust as a Guild Master is questioned which could ultimately lead to being kicked out of the Guild or you could escape your death and contracts would follow suite for your death. Like how assassins etc are sent.
Lead the Guild continuously and successfully you receive a greater cut in the guild's profits, items, recognition and recruits.
Kinda a generalized idea on Guilds. I could be more descriptive if someone cared. I also think it's kinda weird to be Guild Master of all Guilds seems to me it would be very conflicting in the game world. I personally think you should only be allowed to join one Guild per character unless you disband yourself from that Guild providing you leave on good terms.

I would like to add to that you wouldn't have to continue through the option of being a Guild Master but to be one should have more responsibility then just up and leaving to do other things and not returning for sometime. I think it should be optional to be a Guild Master and if you choose to do so is followed my Guild management stated above in vague detail. So you could progress normally but at the end you would have a choice. We all like options and I don't think there was enough if at all in Skyrim when being labeled Guild Master.