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					Originally Posted by 1998Boxsterrr  First off, how common are these issues? | 
	
 
Fairly common. Do a search and you should find several threads on each issue. 
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					Originally Posted by 1998Boxsterrr  Worth repairing? | 
	
 
Definitely. 
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					Originally Posted by 1998Boxsterrr  Is it something i can go given limited mechanical experience (but willing to get my hands dirty)? | 
	
 
Yes, but it will take patience. Some of these are not 15min fixes but they aren't rocket science either. 
For example, you'll have to trouble shoot the SAI system to determine which component (pump, wiring, change over valve, etc) is causing the fault. The trouble shooting can be detailed and a bit tedious. 
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					Originally Posted by 1998Boxsterrr  anyways, looking for some general guidance as to what to do... | 
	
 
Buy the Bentley repair manual. This will help guide you through the repairs. Here is a used one for only $45: 
 Porsche Boxster Service Shop Manual Bentley
Porsche Boxster Service Shop Manual Bentley
Also, buy the 101 Projects book. This will walk you through many common projects. Here is one for $16: 
101 Projects For Your Porsche Boxster
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					Originally Posted by 1998Boxsterrr  ... which to approach first. | 
	
 
I'd start with getting the car to run properly and then work on the secondary issues. 
Thus, I'd start with the  the O2 sensor first. 
Next, move to the Fuel Pump Relay issue.
With the engine running well, then I'd address the brake light sensor. This could be a sensor issue (which is cheap and easy) or the brakes may be worn and in need of replacement. This should be fairly straightforward to inspect and diagnose. 
I'd save the SAI issue for last (which is emissions related and generally doesn't affect the operation/performance of the car).