You should start by doing what you know you can do and what you think you might be able to do, trials bikes are pretty basic and simple so if your unsure of something, you can probably work it out. For things like brakes, if your not sure how to set them up well, you can mount them on loosely so that someone else can basically come along, set them up and tighten them down, thats easiest with maguras. If you have HS33's though, an easy way to set them up is like this; Get a CD or 2, depending on how far you want to pull you lever, if you dont wnat to have to pull it far, use one, if you likepulling it far, use 2. Put the CD against the rim, back the TPA out all the way on the lever then push the pad square against the CD and then check that it lines up with the rim. After you've done this, hold it all in place then tighten it all down. If you do it like this you'll always have perfectly square brakes and shouldn't have any problems with your brakes. Stem, handlebars, bolt on stuff like that is pretty easy and you shoudl be fine. Building the bike yourself is the easiest way to learn alot about bike maintanence and it will help you heaps in the long run!