First, if you are going to strip the paint off your bumper, use a stripper that is safe for urathane. Sems makes some but it doesn't work well on oem (or any baked on paint) as it is much tougher than painting it conventionally.
Second, do not rattle can it. You can get color match rattle can paint but it will not be the same, look the same.
Third, you can paint over existing paint, AS LONG AS IT IS STICKING. If you have flaking, cracking, etc, you need to sand through it. But just those areas.
Lastly, do yourself a favor and take it to a body shop. A good shop should charge $200-300 to do it. If you do all the sanding yourself, you can save a decent amount of cash. Talk to a shop, they will tell you if they are willing to work with a prepreped bumper. They usually even give you tips. Just let them know that you are willing to pay for any work they need to do to get it perfect.
If you really want to get a spray guy, plan to spend atleast $100 (you can get cheaper ones that work but i wouldn't recommend it if you are new to it-advice from friends, i'm just about to buy one). Add on paint, a compressor if you don't have one and you just put in the same as you would to get it done professionally. But you can use everything again obviously. I'd only recommend this route if you are seriously interested in learning to paint.
Cliff notes, get it done professionally.