1. If there is Honda trans fluid, the dealer would have it. I would do some Civic forum research and see what the gurus are using.
2. Always replace the filter. Any auto parts store should have it. If it is a dealer only item, they will tell you.
3. It's not outside of beginner capabilities, but it is a messy job, unless you are lucky enough that a 2005 Civic has a transmission drain plug. You would be surprised at how many transmissions don't. If there is no plug, you carefully remove the drain pan and hope that you get most of the fluid in your bucket. Read the shop manual on the proper way to refill after draining. Some transmissions want you to put in some fluid, run the car, put in more fluid, check and repeat until full. Others, you just dump in the fluid until full.
4. old cotton clothing make great shop rags. Synthetics not so much, they don't absorb enough. Don't over tighten the bolts holding the pan on, if you do it can leak. It's the gasket's job to create a seal, not the bolts. A little gasket sealer goes a long way.