No need to worry about parking, the lot is huge and well signed and staffed. No need to worry about the tide either as it's rare that the parking lot is affected and the staff would close the endangered sections.
If you want to park as close to the Mont as possible you have to arrive very early.
I've been there several times and it always worked for us to get there very early, take our time to walk up and arrive for the first guided tour through the abbey. Check their website to see when they offer that first tour, especially if you'd like an English tour. It changes between high and low seasons.
Haven't done it personally but it might be less crowded if you get there later in the day. However, access to the Abbey and especially availability of guided tours might be limited. They will certainly be offered in high season but limited availability during other times.