Ill be honest with you... I recognize what you're doing so I think I can tell you better! 
The biggest tip I can give you is to start with two coats of rustoleum primer (autobody or clean metal) sanding with 220-320 grit paper between coats. Your problems is that it's uneven all the way to the base coats! You learned an important lesson we all learn in that you can't get away with half-sanding orange peel on glossy black paint jobs (especially rustoleum) like you can others. And rely on lots of paint to fill-in.
The orange peel problem you've got isn't the buffer, its your sanding & wet sanding! Gloss Black Rustoleum (GBR) paint jobs are very hard to get all the orange peel out. It is just too hard to mix & spray rustoleum and have it level 100%.
You need to stop getting ahead of yourself with the buffer. Many PROS here are not going to be able to EVENLY cut down that amount of orange peel effectively with a rotary. Too much work across too much area. You need to GO BACK TO WET SANDING! In the case of GBR, the entire car needs to be wet sanded until dull & chalky. You're not close to the buffing stage!
Get yourself a PC. Im not kidding... With a good aggressive yellow pad <cough> an old one caked with product to make it ultra-aggressive <cough>, or a wool bonnet. Start wit a very aggressive product, like Diamond Cut. You can still take down wetsanding marks and do *some* leveling of paint. It simply takes longer. What a rotary will do in 1 pass, you can take about 4 to do with a PC. That's not a bad thing if you are burning through so much!
The biggest tip I can give you is to start with two coats of rustoleum primer (autobody or clean metal) sanding with 220-320 grit paper between coats. Your problems is that it's uneven all the way to the base coats! You learned an important lesson we all learn in that you can't get away with half-sanding orange peel on glossy black paint jobs (especially rustoleum) like you can others. And rely on lots of paint to fill-in.
The orange peel problem you've got isn't the buffer, its your sanding & wet sanding! Gloss Black Rustoleum (GBR) paint jobs are very hard to get all the orange peel out. It is just too hard to mix & spray rustoleum and have it level 100%.
You need to stop getting ahead of yourself with the buffer. Many PROS here are not going to be able to EVENLY cut down that amount of orange peel effectively with a rotary. Too much work across too much area. You need to GO BACK TO WET SANDING! In the case of GBR, the entire car needs to be wet sanded until dull & chalky. You're not close to the buffing stage!
Get yourself a PC. Im not kidding... With a good aggressive yellow pad <cough> an old one caked with product to make it ultra-aggressive <cough>, or a wool bonnet. Start wit a very aggressive product, like Diamond Cut. You can still take down wetsanding marks and do *some* leveling of paint. It simply takes longer. What a rotary will do in 1 pass, you can take about 4 to do with a PC. That's not a bad thing if you are burning through so much!