Safe to redirect traffic to a parking page?
NO.
You cannot drive traffic to a parked page using any active method.
Traffic must be natural from static unmanipulated sources (type in, existing back links).
You can unpark a domain - restore the site / do SEO / wait / then repark.
But it violates Google's TOS and therefore every parking co that uses a G feed if you send traffic.
Don't quite grasp your 2nd question - do you mean create your own landing page to improve your click thru rate on for sale inquiries - someone else would need to chime on the whole issue of redirects to a custom sales page outside of any options offered by parking companies.