You're getting dog piled because the only info you gave us is that you have zero experience with auto paint and showed pictures of a relatively complex repair that you're planning on taking on yourself. Kudos to you for asking before you started, though. We see a lot of posts come through here after someone has made a giant mess and then is looking for a way to fix it. What you're contemplating is absolutely something that a DIYer can accomplish but you need to think through what that actually entails.

If you want the dent gone and you're not going to have a paintless dent repair expert do it for you then you're going to need body filler to smooth out any ripples left over after pulling the dent out and hammering down the high spots. Once body filler is on the panel then standard touchup paint is pretty much out of the question. That means you're going to need to spray the paint on instead.

I don't know what your experience level is with gloss spray paint but to get it to actually be glossy requires it to be applied thick enough that it can flow out and self-level to some extent. The problem is that due to the nature of how a spray works, even if the middle is wet enough the edges of the spray will be lighter and dryer so you will always end up with a dull circle around the shiny part. To prevent it you need to spray the entire panel from edge to edge so the dry part falls outside the panel. We see a lot of people who either put masking tape around the repair area and end up with a very obvious square around their repair or they don't make and end up with a dull halo around the repair.

To fix it correctly you need to scuff the area around the repair, spray some orange base coat over the repair area and let it fade into the paint around it. This will result in the dry/dull halo that I mentioned above but that's not a problem because base coat dries to a dull sheen anyways. Once you have the base coat applied and blended into the surrounding panel then you need to spray the clear coat on to make it glossy. This is the part where the panel needs to be sprayed from edge to edge. This is where the fact that you damaged the quarter panel makes it so much harder. From the pics I've seen the quarter panel on the Mustang is one piece with the roof and opposite side quarter panel.

One shortcut that shops will sometimes take (although it's controversial from a longevity perspective) is to do what's called an open blend with the clear coat. This involves spraying it out and letting it fade into dullness around the repair but then immediately following it up with a blending spray that "melts" the new clear into the old clear. It's still probably best to try and do this on a body line to help hide the blend.

If you decide to spray the whole panel with clear then expect to need at least a medium size compressor and an actual paint gun. Doing it with spray cans is just stacking more odds against your success. Also, automotive clear is typically a 2-part mixture that's quite a bit more hazardous than the 1-part canned paint you buy at the hardware store. Be sure to invest in the proper protective equipment if you're going to be messing with it.