1998 2.5 Boxster Tiptronic 118k miles 
I recently had a few CEL codes pop up that may or may not be related to this issue.
P0446
P0130
P0150
The two oxygen sensor codes came up a couple months ago and cleared after a couple days on their own.  They came back a few nights ago along with the P0446.  I did have an incident where the gas nozzle did not shut off and overflowed about three months ago.
The starter issues began with an intermittent noise on startup that lasted a fraction of a second and was loud.  It happened randomly about 3 or 4 times over a long period.  While working on my grandparents car it happened before a trip to the store and on the way back.  The next day the car would crank perfectly but not start.  It took a few tries and then ran fine.  It has happened about 50% of the time on all of the starts since then.  I will have trouble and it will stumble, then it starts after a lot of cranking, then I can shut it off and it will start normally.  I also noticed after the first cranking issue that the next few starts seemed quicker than usual and the CEL came on solid with the 3 codes I mentioned earlier.
I'm thinking the starter is not engaging properly but the codes are throwing me off.  Where do you guys recommend I start here?  Battery tested fine on DMM.