tisdallmcphee,
You have pretty much the same schedule as me. I have to leave at 6:30/6:45ish. I treat the feed right before I leave as a night feed. This puts me off easy a little bit. Below is my schedule:
6:15 Feed, put back to sleep
7:30 DH takes DS to daycare (consider this activity time)

He normally takes another nap in here
10:15 Eat (expressed bottle)
Activity
Sleep
2:15 Eat
Activity
Sleep (cat nap) DH picks up from daycare around 5:00 so he wakes up for a while after his nap
6:15 Eat
8:00 cluster feed put to bed
10:00 df and cross our fingers until morning.
This is 4-hour easy. When we were on three hour it was the same thing but he ate at 6:15, 9:15, 12:15, 3:15, 6:15 - it is perfect because I got the 6am and 6pm feeds.
As for the freezer stash. I pump as much as I can at each session and don't throw anything away. I have a lot stored and figure that it is always better to have too much than to little. Here is the problem. You want to avoid supplimenting with your freezer stash as much as possible - it is downward slope. The stash should be used for if you have to miss a feeding you didn't intend to miss. If you suppliment with the stash then your LO will not be able to tell your body that it needs to produce more milk and you will keep under producing. I haven't really had a problem in this area, but I would say if you are within an ounce of what your lo would normally eat then just give that amount.
With the above schedule my ds has adapted and seems to take less during the day. The 6pm feeding is the longest of the day. I think mainly because of the missed suckling time. When we started daycare, the only word I could use to discribe this feeding was "ravenous" - I felt like I was starving him during the day. Within a week he totally calmed down - this is how I realized it was a suckling issue and not a hunger issue. Once he was comfortable with the change in his lifestyle all was good.
Good luck!