I don't know if it has any sort of protection circuit. They've been available for at least a few years, the battery in my WR originally went in my SV1000 in March 2013 (it has a custom subframe so I needed something small). It'll start it no problem, and if there's a bike problem it'll crank for quite a while before slowing down - probably in excess of a minute (I was having trouble figuring out the starting problem, it was a tipover sensor). When I found the WR used the same battery that I chose for the SV1000, I decided the bike that's electric start only with a bigger engine deserved the new battery.
I have an RG3 top clamp on it, with a 4 point rubber mount setup that eliminates the buzz and doesn't let it move around much.
That shows the one I had with stock forks, I've since upgraded to 05 YZ250F forks/triples, but the concept is the same. If you end up with an 03 WR450 (or anything else that uses the same top clamp, I don't know if there is anything) I'd be happy to get rid of the clamp pictured. I might have a set of wheels available too, or I can point you towards someone else - I know Stainless601 had some nice ones available at one point.
I think the most highway I've done at a time is 35 miles. It certainly isn't the most pleasant bike for that, but it isn't horrible. I'm geared pretty tall, at 14/40. 17s mean that isn't as outrageously tall as the same gearing on stock wheels. I have a 15 front but haven't tried it, it wouldn't be as much fun. The seat isn't horrible, but not great either.
And yeah, not only the bridge but then getting home too... I could run lights occasionally, as it did charge, but didn't run them unless I felt it was very important. Luckily there was a full moon, 10 miles at night with minimal lights isn't fun.