Depending on the topology of the model, you appear to be on the right track by providing drain holes in the model. I'm not sure why you feel it necessary to split the model, unless you expect it would not fit the expected build volume.

Do you know that the service you are going to use will not properly wash and cure the model? I would expect that such post-processing is part of the service for which you pay. They can confirm this, of course, prior to your contract.

If your plan includes priming and painting the model, the resin choice should be aimed at physical characteristics rather than color. There are resins available for flexibility, for low temperature melting point (casting) and other characteristics, which should also be provided by your service choice.

It's likely you won't have to sand the model if your layer height selection is high enough resolution, as the primer is going to fill the gaps. You should expect light sanding to be required for the primer.

Good luck with your project. You appear to have done much of the necessary homework to ensure success.