Hi Max, and Welcome,
Brian's advice is quite sound, read through the forum posts, and the build manual until you are confident, then you can start to proceed with the cutting out of the panels.
There is loads of advice and tips through-out the forum on the pitfalls, and as Brian says, don't rush as this will end with expensive mistakes.
Most of us on here have built these as 'Winter Projects', and they have taken, on average, about six months to complete.
I built mine (Harvey's) from a mobility scooter, as did Walter (Multisync), and the best advice I can give you in regards to this is, buy the scooter before cutting out the Rear Inner Wings, as the positioning of the Transaxle is markedly different to the positioning of the Wheelchair motors that Richard uses!
If you do start building before you get the scooter, and this is acceptable, just screw the panels together temporarily, DON'T glue them, until you are quite sure of the placement of the scooter parts. This way, you can dismantle the tub to make changes, without struggling or serious damage, as wood glue holds pretty firm once set, as one or two of us can bear witness to.
You might find my build website useful reading, just click on the 'Globe' icon below my forum name (markh15) at the top left of the reply window, and this link will take you straight there.
Take your time, and above all have fun doing it, any more questions, just ask.
Regards,
Mark.