You know one specialty of Ars is that it is focused around the covenant. So usually you as a PC dont want to go for long trips, or walk around in a DnD style "adventures without roots and meaningful social contacts".
All trose years long skips in the timeline, long trips far away from the covenant, etc should be done by mutual consent among the players and also between the players and the GM/GM/SG.
I think it is important to graps that this style of play can function better if you dont want your players to hook on a certain quest, but rather present them 3 different kind of problems connected to the covenant which are happening at the same time. That is how the players have to prioritize problems and manage resources.
The same you have to do as a SG. Feel free to handwave a couple of things. For example if the PCs want to go from your normal Rhine/Provencal/British Islands tribunal to Mythic Scandinavia, just handwave the length of the route - if they do not use magic - and say that OK, you need 2-3 weeks to and another 2-3 weeks from Scandinavia, so to do some meaningful stuff there it is a 2 seasons trip minimum.
Use the seasons system instead of trying to calculate everything properly.
The most valuable resource of this game is time itself. Seasons. That is the only finite thing your PCs cannot generate more of. You have to understand it and let them understand it also.
Things, mainly local political stuff with the nobility and church, and Tribunal things have to move on and change a little bit. Thats how the PCs can get the feeling that they have to manage time itself: Do we want to go to an adventure to Scandinavia for 2-3 seasons instead of going to the Tribunal? Hard choice.
Gaps can be filled with jus study for the magi. Or if you want to add some new flavour, consider using companions. Ex: The Magi Council ruled that a certain problem is not important enough for the magi to handle it personally, so they send som grogs or companions. Let's give grog character sheets to your players and give them the experience that somebody has to bear the consequences of the choise of the Magi Council.
Personnel changes can be weaved into the story: one mage received a one in a lifetime opportunity to do something, so s/he left the covenant. Now the PCs need a new mage to have the numbers in the tribunal/in the council.
Long distance: BEST STORY OPPORTUNITY EVER! 
Let them go for their long walk of adventure. When they come back, present to them all the shlt happend during their leasuretime as an adventurer. New problems to solve, new strategies to form, a lot of - hopefully - ingame discussion about how to handle things in the covenant when they are abroad. That is kind of an important piece of the Ars M* style (based on my understanding WHY and HOW it is not that other game ).
For filling gaps you can always use previous events as a story seed. The Council sent some grogs to gather Vis, deliver an item of importance, defend somebody who is important, or just accompany the new scribe from the nearby city. Now you can give them grog characters and have some fun. That's how receiving a new scribe to the library can be more fun and can have a taste and smell - instead of just seeing the whole thing from the magi's elevated point of view let experience the adventure! 
And yes, companions are a key component. However: grogs, companions and magi are on totally different power levels. That is a thing to consider.
Magi always have the problem of the gift. Keep it that way, use it, don't give in to temptation of sweep it aside! That is the strongest check and balance on the magi.
Companions are usually weaker than magi - even the mythic companions. Design encounters specifically tailored for their abilities and Personality Traits.
Grogs are like...grogs. You should use your best RPG skills to have fun, bc those guys are weaklings, so let's roleplay instead of rollplay! Any meaningful adventure for grog characters has to consider that they are not even on the same continent as the magi or companions if you have to handle combat. But their big adventage is that they do not have the Gift (penalty) and they know important mundane things. Blending in a normal village, gathering some intel in a town, etc. You as an SG can design problems with time pressure for them, bc from the grog's side a wise strategy would be just call the magi when facing some serious problem. But with time pressure they have to act themselves.