Pedals are not intrinsically self-tightening. If they are tightened sufficiently in the first place they will not get tighter by themselves, at least not in the sense of rotating further into the cranks. You can confirm this by marking the pedals and cranks and monitoring them over time.
The fact that the left pedals have left hand threads is largely historical. A properly tightened pedal will not come loose even if the left hand pedal is RH threaded. This is proven by tandem riders who use RH cranks on the left side. There is still a small benefit to LH threaded pedals in certain circumstances, such as if the pedals are already too loose, so overall there is a small benefit of the LH threads, but the thread direction by itself is not contributing to your problem as long as you put the correct pedal on the correct side.
If pedals are difficult to remove it usually means they suffered from corrosion or they were simply overtightened. In rare cases the crank arms may have been damaged by impact or bending that distorts the pedal threads. Pedal threads can still corrode even when greased, especially if they are threaded into aluminum. Basic grease often contains enough water or other conductive ingredients to allow electrogalvanic corrosion to take place. To avoid this further you can use specific anti-sieze compound or at least dielectric grease.
When installing pedals it's recommended to use grease or anti-sieze. Tighten sufficiently but not excessively. A standard pedal wrench like a Park tool pedal wrench should be the right length so that the tightness will be about right if you tighten them about as tight as you can get them. Do not use a cheater bar or wrap a rag around the pedal wrench when installing, but you can try either of those things when removing pedals.
It's not usually recommended to remove and reinstall pedals just to avoid seizing. But if you are having specific problems then removing, cleaning, re-greasing and properly reinstalling would be a reasonable thing to do, perhaps once a year or something.