Discussing the ins and outs of WD-4 for gun care can be as tiddious as discussing religion or politics; some folks swear by it, some swear at it.
I've used it for nearly 50 years for cleaning and loosening stuck gun parts, but in truth it was not designed to be a lubricant as it will dry out. The WD stands for Water Displacement; as that is what it was originally designed for in NASA's space program.
There are many good gun lubricants on the market. My favorite for the last 20+ years has been BREAKFREE CLP which is a Cleaner, Lubricant & Protectorant.
First off before you work on any guns you need a decent set of hollow ground screw drivers designed for this purpose; and then, use only the proper sized one for the job.
As to your stripped side plate screw, I'd strongly suggest you take the gun to a local gunsmith who has the proper tools to remove it without further damage to the gun. He'll probably charge a very nominal fee for this service.