think 99 will be a ARZ engine take the engine cover off and its on a little plaque beside the timing belt cover. will be a k03 turbo
yes the 03s is a direct swap but uses the lager compressor wheel. in short its a halfway between the 03 and 04
the cone filter doesnt really matter as long as there is a good air supply to it.
wouldnt bother changing the cams unless your looking for massive gains.
just watch as the engine is now over 10 year old so reliability could be starting to get compromised.
costs - k03s turbos normally go for around £2-300 on ebay from breaking cars. DONT TOUCH THE CHEAP NEW ONES these are far east copies and very veiw seem to have lasted more than a month with those who have got them.
remember you will need a remap after fitting to get the best from it. or if already mapped it will need tweeked
brake uprade - your looking at around £150 for the 312mm discs. pads (as long as you dont go to VW as they want £85 acording to my ETKA for a front set alone ) are around £40-60 for semi decent sets
carrier can be gotten from ebay or breakers for around £70
the fly clutch is around £230 iirc - it doesnt fit mine, my upgrade to a SMF and clutch is closer to £1k
intake pipe is around £70-100 depending on make
forge 007p is around £80
rear anti roll bar around £150
as for taking it to a garage, the turbo is probably the only mod there that will cause issue with bolts being hard to free and limited space.
brakes, PH3 screwdriver for the disc. 18mm spanner and 7mm allen key for the carrier. litteraly is around an hour max even if you dont know what your doing. give longer if your changing the pads.
the diverter valve is a 5 min job. remove engine cover. cut off the clips that hold the oem one in place pull out new jubille clips on and fit the new valve.
try and find a vag specialist that knows what theyre doing with the 1.8t engines