Hi there. When there is white smoke emitting from the exhaust system, that is a sign of coolant in the exhaust system. Check the coolant level and see if its low. If the coolant is low, then check the engine...
There are many options on the market today that only a muffler replacement (https://www.yourmechanic.com/article/how-to-replace-a-muffler-by-robert-tomashek) will improve the sound. You can go on some web sites and they will have sounds of the muffler (https://www.yourmechanic.com/article/how-to-choose-the-right-muffler-for-your-car-by-brady-klopfer) they have for sale to give...
This sounds like it is something that is within your skills ability. I can't speak to your skills for certain without knowing what kind of repairs you have done in the past though. As far as oil pan gasket replacement...
