I hope you take up the challenge. I wish you success with the IVA test, I did its predecessor the SVA test for my 3000 kit in 2004, so I am out of date but I believe the IVA is not hugely different. It may seem daunting but don't be put off. As Ian says read the IVA manual lots of times to take it in, it will make you understand the alterations that you will need to make, and will save you money and time in the long run. The thing about kit cars is that you spend can a lot of time doing things over if you don't think through all the implications of changes. To give you an idea of the content it covers things like
The height of all the lights, the spacing of lights.
Mandatory lights rear fogs etc
Curves of all the external features.
Design of Mirrors and position
Protrusion and design of door/boot handles,Hinges,
Wheel being inside the body
Cockpit switches
cockpit instrument lights markings
curves and protrusion on the dashboard
Security of the cable loom
Whilst I painted my my car before the SVA, I would advise against it because if you did end up making any alterations to the car for the test it would make it more difficult .
I urge you to take on the challenge, the reward of doing so is amazing, I had to go for the retest after failing on some points but it was an amazing high driving home, at least it was until my brake caliper seized on the way home!