Hi Glenn and SG,
Welcome back, Glenn, good you are working on a U-boat related model. Firstly some background. The Fa330 was tested on the IXC U 523 in the autumn of 1942. U 523 had a yellow training band at that time. These images show U 523 at that time -
U 523 had the Turm 0 tower at that time. U 523 was a Type IXC but due to size the kite was only used operationally on IXDs. SG's image of U 852 shows U 852 (IXD) during commissioning with a Turm II. The U 848 image shows this IXD boat with a Turm IV. I don't think any IXDs had the Fa330 with Turm 0. But you can go with U 523 as the photo shows how the platform was attached to the top of the railings.
In regard to railings, have a look at these two images of U 68 and U 128 respectively -
To answer questions 2 and 3, you may recall that the top horizontal bar on VIIs was thicker. On IXs it looks like the top horizontal bar was the same diameter as the middle horizontal and the verticals. In 1/16th scale these might be somthing like 3mm in diameter.
There was an additional horizontal bar near the bottom. The blue arrows on U 68 show either side of this additional bar. It looks like this bar was thinner than the rest but you can judge for yourself.
There was also another exception. One vertical railing on each side (pointed to in red) was much thicker at the bottom than the top. It starts off at the top the same diameter as the rest.
Note there was a one-piece wooden seat on either side, with the vertical railing bars going through the seat.
The hard part is working out what U 523 had inside the wintergarten platform. The boat was working in a test capacity so there was not a requirement for the 20mm anti-aircraft gun. They would need space to assemble the kite. It looks like the 20mm including the 20mm mount was removed from U 523. It looks like one crewman is standing on something that is located where the 20mm would normally be. It is likely to be equipment associated with the Fa330 but it is hard to tell what it is. The Fa330 may well have been stored inside U 523 without there being a waterproof container in this location.
Is your question 1 asking the diameter of the wintergarten railings (in other words the width from one side to another)? This would be about 220mm in 16th scale. Additionally the width of the wintergarten floor would be around 166mm in 16th scale.
Cheers,
Dougie