I mostly lurk around here, but couldn't resist this one. I am on my second e92 M3, one was manual transmission and current one is DCT. Prior to the M3, I had never owned a German car before, so I was worried about maintenance, reliability, etc. My experience has been great so far - I have never had to do anything other than routine maintenance - brakes, tires, oil, brake fluid (all of this compounded by time on the track). No other issues - not a single one. The e92 M3 (or e93 in your case) is extremely reliable, BUT if something does go wrong, expect it to cost an arm and a leg. Example, my buddy just had a problem with his oil pan that seemed pretty basic - it was a $2,300 fix at an indy shop. There have also been a number of issues with rod bearings causing engine failure, which is about a $20,000 problem (rare, but catastrophic). For that reason, I have always maintained an aftermarket warranty.
As for maintenance, expect everything to cost more. Oil change at the dealership is about $300, but you can do it yourself for about $120 or about $200 at an indy shop. Brakes are $$$$ - about $1500 for 4 corners of brake pads and rotors. Tires can be expensive as well - plan on $1300.
That said, I am in love with the e92 M3 - I am convinced there is no other car that can do DD duty, comfortably put kids in the back, and go all day at the track for about $40k. It is a beast on track and the sound is intoxicating (especially with an aftermarket exhaust). Engine winds to 8400 RPM.
I suggest you drive both the manual and the DCT. My first one was manual because I was convinced sports cars only came in manual (or should). That said, the DCT gets so much more out this engine - shifts are so fast and so much fun - only thing similar is Porsche's PDK. It is awesome.
Another thing to be aware of is that the car is a blast when driven at the limit, but is very tame otherwise. You have to wind this engine up (over 5000 rpm) to really feel the power and have fun - which is very hard to do legally. A 335i or comparable car will feel faster around town with higher low-end torque. So if you don't plan to take it to the track (I assume not - convertible), you may want to consider that. Either way, the car is a blast, just don't expect it to be a stoplight racer.
Finally, as to that specific car. I think the price is too high. Convertibles sell for much less than the coupe or the sedan versions as they are much heavier and have become less desirable. For reference, earlier this year, I paid $40k for my e92 with competition package, fully loaded, 21k miles and a full warranty through the end of 2019.
Let me know if you have any other specific questions.
