Trying to decide whether to replace/augment cyclecomputer and cuesheet setup due to presbyopia (can't see up close due to old eyes) or maybe going total Fred and buying industrial safety glasses with built-in bifocals.

With respect to the Garmin 810 or whatever the newest model number, could anyone provide some insight/experience to any of these questions? Sorry these are very naive questions. Thank you for any help.

1. Can I connect an auxilliary battery source to run an 810 on longer rides? If so, how good is the seal to keep water out?
2. How good is it at keeping me on a fixed route or does it recalculate automatically? If the 810 does recalculate, can this feature be disabled? I read somewhere that the Garmin software people screwed this up on a version of firmware. Forced re-routing would be a dealbreaker.
3. How are the standard maps on it? If I enter a destination, will it route me over good cycling roads? Or do I have to sit at my computer and map out a route and download it to the garmin?
4. How easy is it to load custom routes using a PC say if someone gives me their route?
5. Is the screen resolution and font size sufficient for old eyes?
6. How waterproof in general?
7. is the speed and distance accurate?
8. Does the 810 heartrate function get confused by powerlines or other cyclists' HRM signals?
9. What are your favorite features of the Garmin? Would you buy it again or in retrospect would you stick with a cue sheet and cyclecomputer?