Good morning to all who reads this. I've recently just acquired a really cheap but,(new n to me 2005 Buick LeSabre custom. It has around 200,000 miles on the clock and is fairly clean inside and out. The only issue that you pull up for is to have is one thing to the front driver fender and the check engine codes: p0350 and p1350. I would like to know what are some mechanical issues that I can expect around this mileage that I should take care of aside from general maintenance? If at all possible i intend to keep this car for a good while and maybe do some real mild mods.

P0350 = bad ignition coil
P1350 = bad Ignition Control Module (ICM)

For this, I'd change out all the coils and the ICM.

Long term: Look out for the front wheel bearings to start going out, and service the transaxle. If you don't know the age of the belt then change it and keep the old belt as a spare. Otherwise keep up on maintenance and don't abuse it and it will probably last a long time.