I understand your frustration; I have had a love/hate relationship with my B5 as well. I have gone through failed MAF, ICM, and 3 window regulators, … be patient, the B5 is a very enjoyable car to drive (which you already appeared to have learned).
If you do not know the maintenance history, you may want to run it through an Auto-Rx treatment, just to head off sludging problems. Either way, it is cheap insurance for a 1.8T.
There are many people around here that will help you diagnose problems yourself, if you have the time and patience (it will save you many $$$$). Be sure to use the site’s search feature. Most questions have been asked before and answered by some very talented/knowledgeable people.
I purchased my APR chipped ECU used from a member off this site. You want to correct the ECU box’s harness protectors before you install the new ECU. The box is watertight for a reason; that is why the wiring harnesses have the sealed rubber boots. This condition may have attributed to your ECU’s demise.
If the chip is an APR, you can have the chip changed to an automatic. APR charged me $50.00 to perform the change and transfer the lifetime warranty into my name. I sent SilverBullet the money; he shipped it directly to APR. APR changed the chip’s transmission setting and mailed it back to me.
You just have to make sure that the ECU serial model will work with your B5. If you have the proposed ECU serial number and call APR, they will tell you if it will work with your model/year car. They did this for me, even though they were not making the direct sale, only the pass through.