I couldn't resist doing that. You had lots of very broad questions and no one answer fits all. For example; there are different 'limits' on entering and leaving Mexico which depend upon your immigration status. FMT is a single entry document, FM3 has no limits, FM2 has limits, etc. You may not leave your car in Mexico if you leave and only had an FMT. You need an FM3, or better, for that. In all of these cases, I refer to the interior of Mexico. The frontier zone, a few northern states and Baja have unique rules. If you have a reliable car which is also popular in Mexico, you may keep it registered somewhere in the USA and use it in Mexico on an 'importada temporal'. Eventually, it will have to leave and you can't ever sell it in Mexico. Otherwise, there are lots of cars available in Mexico; new or used, if you have an FM3 or better. Rentals are available in all price ranges and one's social life is what you make it. At Lake Chapala, there are more than enough things to do; concerts, charitable events, local entertainment, fiestas, parks, malecons at lakeside, restaurants without end, day trips, etc.