Do all the calculations, and don't try pulling a trailer too heavy for your truck.
Weight on a trailer equates to size of the RV. The biggest thing to consider is your comfort zone. You won't be in tune with that until you actually start towing. I started out being a nervous wreck, and emotionally drained after a day of towing. That does not make for fun. Your comfort zone will be determined by driving in heavy traffic, being able to back and park, and in general, gaining experience. I'd recommend buying a 5th wheel that will more than meet your needs, because those needs will increase with time, and one that stays within the towing specs of your truck. Being in bumper to bumper LA traffic, trying to change lanes for your exits, and having vehicles knife in front of you as you try to maintain a safe distance is not a good way to start. That's why it's important to make some short trips while you gain experience and confidence. Good luck!