Hey Rene,
I operate a STR in Mt. Pleasant and found the licensing/permitting to be easy to navigate. You are correct that it is limited to 1% of the homes in Mt. Pleasant which is good and bad in that it limits potential competition, if you get a license. The lure of Charleston is the beaches and downtown so you typically want to be close to both of those to get a good ROI in my opinion.
I would suggest you get on AirBnb or check out AirDNA to see what places are renting for right now and the occupancy rates. Make sure you have reserves for another major shutdown in case we see a repeat of March - May where all of our bookings dropped off.
North Charleston is more up and coming and probably not a great AirBnB area outside of maybe Park Circle. Downtown you are limited to the STR overlay district but that's way out of your budget and not sure it would provide a ROI even if it was in your budget.
Can you build an ADU on your property to rent out?
Also, if you want a local realtor who grew up here check out the Beach Company - Chris MacEachern, Will Freeman, Sam Little, Russell Robinson, etc. I've known all of them for decades growing up here in Charleston. They are all well versed in STR and investment property. I've personally used Chris a few times for investment properties.
Best,
Brandon