My .02,
Use components that came from cars with mechanical controls. Im talking about the type that used cables attached to the knobs you were turning. This will make adaptation between components and controls easier, allowing you to mismatch in your favor. Also, look for modern cars as donors, so you can recharge easily. Your going to end up fabricating, so don't limit yourself to Nissan unnecessarily, Honda's apparently have components similar in size to the s30 pieces they will replace, so that might be worth exploring. Also, some car models are available with AC control relocation panels (usually used when you need a double din for ICE but, the kits are usually in a din format themselves. This might make it easy to get controls into the S30 dash without any cutting or fiberglass, etc...