Use which you like. If you don't like it, then it's not the right decision.
2. Gaming, heavy video work tends to get the desktops. For this 3D printing, from what I see, a laptop is fine.
3. Your choice. The office just goes with the usual 500GB to 1TB drives that come stock.
4. The software is what you can use plus works with the system you are driving.
5. Harder area. For some the plastic making bot is what they need so you should know this first, not last.