Our AUA had a lambda sensor and catalytic convertor that needed to be replaced last year. It appears (in retrospect) that this was secondary to the car running rich on at least one cylinder and chucking a lot of fuel into the exhaust, largely because of age / mileage and lack of servicing that resulted in worn / dirty injectors, the EGR / throttle body being full of tar and an intermittent misfire (old plugs, old cables, coil severely compromised due to age (cracking in the casing meaning that sparks were being lost).
Compared to an FSi - though which you obviously have a lot of experience of - the solution to get an AUA running sweetly appears to be relatively simple and will be well within your capabilities ; I replaced TB & EGR, spark plugs, cables, injectors were sent to Injectortune to refurbish, new Bosch coil, and the oil catcher (if this hasn't been cleaned, the throttle body and plastic casing above this will be extremely oily). If you're lucky, the various bits of pipework between air filter and the TB will be intact and not cracked. I was able to do all of these which demonstrates that they are utter childs' play compared to anything like the FSi intake manifold and the things you've taken on.
Hopefully you won't even have to replace the majority of these, although doing all of them would probably be a good idea with a car of any significant mileage (ours was on >185,000 and I suspect most of the above were original!).
Best of luck!