Just stay hydrated. Always carry a bag with a few water bottles. :)
I go on 2-3 mile hikes almost every day of the weekened. Keeps us busy and my 4 year old loves the outdoors.
Its OK as long as you don't overheat.
If you have been consistent before and during pregnancy you should be OK. My friend did marathons at 8 months.
However if you are not used to that you may feel it later. Cramps and over tired. I usually get it right away if im over doing it. You can't hurt the baby by over waking just your self. Unless of course your close to the end and have had pre term issues.