Welcome to the forums! I can only answer from experience of working on Pak128.Britain; Pak128 may have somewhat different alignments.
However, assuming that there are no significant differences, firstly, it is sensible to download and install the latest version of the automatic rendering script here
Secondly, the easiest way to produce objects for Pak128.Britain is to start with one of the existing .blend files (available here
and adapt them as necessary. This is because the camera and lighting is already set up precisely and no further work in that regard is required. The lighting may be different for Pak128: one of the Pak128 developers should be able to assist with that. Do not worry if you have already created your own models: you can export these as a Collada (.dae) file and import them into one of the existing .blend files with the camera, lighting, etc. already set up. The rest of these instructions assume that you have done that.
Thirdly, I advise in favour of using the new alpha transparency workflow, which makes things much easier. Hopefully that should not be a problem in Pak128: it certainly works well in Pak128.Britain. To do this, make sure that "RGBA" rather than "RGB" is set under "output" in the render options (the camera icon in Blender). You then do not need to undertake any post-processing of images for vehicles and single tile buildings at all after rendering them from Blender.
Fourthly, the settings to use depend on whether you are making vehicles or other objects, and, if vehicles, whether you are making road vehicles or other types of vehicles.
For vehicles other than road vehicles
, you need to use the "Render 8 views vehicle alignment" setting in the "Rendering views for Simutrans" tab created by the Blender plugin. These will not need offsets specifying in the .dat files. Assuming that your vehicle's image files are named "example-vehicle" and they are in the /images subdirectory of wherever your .dat file is located, you will need the following code to reference the graphics in the .dat file:
For road vehicles
, , you need to use the "Render 8 views normal alignment" setting in the "Rendering views for Simutrans" tab created by the Blender plugin. You then need to apply offsets in the .dat file as follows:
When producing multiple vehicles, you can just perform a search/replace on the names so as not to have to keep typing out all of the offsets, etc.
For single tile buildings
(city buildings, extension buildings, etc.), you need to use the "Render 4 views normal alignment" setting in the "Rendering views for Simutrans" tab created by the Blender plugin.
Single tile buildings do not need the use of TileCutter, but do need a different .dat file syntax: it is best to adapt a precedent .dat file in the code archives. Multi-tile buildings
(such as large industries or attractions) do need Tile Cutter. Tile Cutter is not compatible with transparency, so you will need to use the old-fashioned workflow for the present, which I believe is described in other threads relating specifically to Tile Cutter.
The automatic rendering script is not suitable for use for making ways, way objects and certain other specialist graphics, but Blender can still be used to create these (just export them manually for each rotation with F12/F3).
For vehicles, make sure to get the positioning and scale correct. I do not know the positioning or scale for Pak128, but for Pak128.Britain, the positioning requires the front of the vehicle to be placed 4 grid squares in Blender in front of 0,0,0 (the crossing point of the red and green lines) and the scale can be derived from a special ruler (a .dae object) which represents a length of 15 meters on the y axis (the x and z axes are scaled 1.25x in proportion to the y axis) can be downloaded here
. This ruler can be imported into any .blend file and used to scale the objects.
I hope that you find this helpful; best wishes with graphics creation for Simutrans. It is a splendid way to spend one's time.