Dude... i suggest you read up more on turbos... how they work, this that, etc in order for u to fully understand what it is you're doing to your engine, then you'd know how the wastegate works.
Most OEM turbos come with built in wastegate. The reason for an aftermarket external wastegate is either:
No.1 - your turbo doesn't come with a built in wastegate (like BIG aftermarket turbos)
No.2 - your built in wastegate not big enuff for the amount of boost you're running... therefore you'll be experiencing boost creep, where your boost towards high revs will creep up (usually happens when u boost much higher than your actuator settings).
Choosing wastegate size is like choosing exhaust piping size. Too big no good, too small no good.. gotta pick the right size for the right boost on the right turbo. =Þ
If you're using a TD04 or TD05, the stock actuator should work fine up to 1.2 bar or so (about double the stock settings)... if you're boosting like 1.5 bar... then safer to get an external wastegate... 38mm one should be enuff. I have friends boosting 1.5 bar on a TD05 without problems without the wastegate also, but i think better to get external wastegate lah if boosting that high... the last thing you need is for your boost to creep! hehee..
Wastegates are MECHANICAL devices... got nothing to do with the emanage. If you buy 1 bar punya wastagate, its gonna be 1 bar. Can be adjusted with a boost controller, but not the emanage.
Personally... i've been to Dragger Racing... and I've spoken to Andy... and i too agree he's a very nice guy to talk to, and he as well explains everything A-Z to you to make sure you understand every detail of the bolt on before he begins his turbo works on your car.
I do highly recommend Dragger Racing for bolt on projects... BUT, i'd only recommend their stage 1 bolt on lar. Their stage 1 bolt on kit is quite close to complete... after bolt on their kit, all else you'd need is to slap in a new exhaust system and a good engine management. Tuning DOES make a BIG difference, no joke on this one.
i wouldn't recommend anything other than their stage 1 bolt on... coz' I believe if you were to want to expand your performance, and want to squeeze more power from your engine and turbo kit... you'd have to do it on your own from there on. As in, you should be then fully understand how the engine and turbo works, and you should by then know what and what can be done in order to squeeze more juice... don't have to rely on packages wan.
Anywayz... have fun exploring dude. =)