Battery preservation and multi day route options..

I think the main thing to preserve battery life is to set the brightness as low as you can get away with. I suspect that experimenting with Bluetooth accessories is potentially the next most effective; I’m not sure that PMs, cadence, HR, etc make much difference, but certainly pairing an iPhone seems to wallop it with recent versions of Connect. I’ve taken to using my (work) Android phone (understanding boss!), which is more efficient. Experiment. Navigation also hits the battery, but it sounds as though you need that. Leaving the map display on permanently uses more power, though, so avoiding that would probably help. 

As for the courses, I’d definitely use a different file each day. They will load faster, and are much less likely to cause you problems. Given that you’ll be able to store as many courses as you’re likely to need, there’s really no advantage in doing anything else. Personally, I’d also record each day separately, too, though you may want the “cred” of a really long ride on Strava. Personally, I’m not sure that it proves a lot - I could just leave my GPS to record a month’s worth of commutes, but it wouldn’t make one very long ride - and recording one huge file is tending to send your 1000 wobbling into the unknown! If the file corrupts, you might lose the lot. 

In the past I've used a small usb charger strapped to the frame which can charge the Edge 1000 during your ride to keep the battery topped up.

Definitely use routes 1 per day, as mentioned it will be quicker to load.

Split the route. 

Use an external battery. 

I used to attach a Jackery Mini "lipstick" battery to my stem with electrical tape, and use a short microUSB cable to attach it to the Edge 1000.

Consider this: Yesterday, Garmin announced their Holiday Sale, and the Edge 1030 is reduced by $150 to $449.  It has great battery life.

Build your courses in daily chunks, or even two per day.  The courses will load faster, and if you get off course or need to detour, they'll recalculate faster.  You can delete each course after you complete it.  And your actual daily ride doesn't have to conform to the courses you use to navigate.  (But I'd try to save the .FIT files after each ride, just to be sure you don't lose them.)

A lipstick size battery is great. Small & light. 

I turn off BT and have the brightness set to off which is fine outdoors. 

My battery seems to deplete by 1% per mile or so. So really only need to think about topping it up if riding 75mi plus. I just plug the lipstick battery in at coffee stops etc. Seems to give it a 10-15% boost in 20 mins. 

Another tip if not charging it at a break, hit the pause button then tap the top left power button and it will go to sleep but won’t loose your ride. Re tap the power button and then the pause button to continue the ride. 

Only proviso is the power button is famously fragile, i press it as gently as possible to try to prevent the cracking problem.