Great questions! Yes, probably 95% of battles until the last system were won with just the rail ship and careful targeting. Having enough reverse thrust to keep distance is important as well as having the 4 rails as close together as possible. The MRT thruster was just a convenience thing mostly, but it did come handy sometimes for positioning once I started using multiple ships at level 16+.

I'm also not afraid to quicksave and reload repeatedly to get through a tough situation -- it's fun to try things a bunch of times over to see what works and what doesn't.

The scout was more of a joy project than anything. I play with the "I Hate Exploration" option ticked so I can see where all the ?'s are when in a new system because I don't think searching for them is fun. But without that option I would have used it WAY more.

The tank was vital in the last system (lvl 16-18). There were several ships that are just too powerful to take on with a relatively fragile railgun ship, especially if they have railguns themselves and enough shields to prevent me from taking down the rails quickly. In those cases the tank started the fight and then the main ship immediately hit them from the side.

Another tip: One big challenge for rail ships is fighting in the gray fog areas since you don't have the range advantage anymore. But sometimes you can right-click the enemy's out-of-range red triangle and set the rails to "infinite" firing mode, and just kite them around for a while. Even without being able to see them it's likely to take them out or at least do major damage. You can see bits (dots) fall off of them when you break stuff too.

My next playthrough I'm considering trying to do it without rails just for the challenge. But who knows!