I have been 456 GTA owner for 7 years here in Tokyo, Japan.
I did timing belt replacement last December by myself, but not alone. With full support of a pro Ferrari FR V12 expert "AkaiAkuma". https://minkara.carview.co.jp/userid...blog/40812622/
When 8 456 owners gathered last year, there was no Rosso Corsa. https://minkara.carview.co.jp/userid...blog/40733702/
But I saw at least 2 456s Rosso Corsa , and they were great! So, don't hesitate to ride on a red 456.
As mentioned in the second blog, window is a weak point of 456, 456M seems improved.
You may already know other fatal point of 456, that is in gas tank area. Plastic fuel pump cover breaks and gas leaks. That part is discontinued, so I asked AkaiAkuma, and he produced metal cover for us. https://minkara.carview.co.jp/userid.../blog/m201404/
Also, fuse board might be damaged but I'm not sure it's caused only under Japanese high humid climate. AkaiAkuma also made fuse board for us in 21st century Japanese quality.
Other than that, of course, usual maintenance is required.
Such as oil, fluid, rubber for hose and suspensions, shocks, battery, some bearings, filters. As they are already 15 or 20 years old, and high temp under hood w/ V12, rubbers and other chemicals might be damaged including o-rings for A/C.
With parts, you can DIY almost everything, if you have a good adviser around you.
I hope these info will help your decision.