[Humabout]

For scale reference, the Milky Way is 1 to 4.5 kiloparsecs thick, so you're looking at a pretty insignificant volume, which seems to fit the feel you're going for. It's also a scale I happen to like, personally.

As far as travel speeds go, consider that the effective average travel speed is usually what is most important - not the per day speed. If, including stops for heat dissipation and charge, gives an average speed of 1.5 parsecs/day, build off that figure. You will also want a max sprint speed and sprint range (PCs will inevitably ask this and factor it into their plans.)

Some general worldbuilding-type questions:
1) When a ship uses FTL, does it travel through real space? Does it have to dodge planets and stars and stuff? Does it enter another dimention/universe and travel there? Does anything live there? How does that universe/dimension differ from ours? Does it need special fuel/material (dilithium crystals, hyperfuel, negative mass materials, etc.)?

Frex, I have a drive that momentarily transports a ship to "hyperspace" and then blinks it back in at another point in our universe. Stuff does live there and little is known about hyperspace. The laws of physics are very different, and it isn't particularly condusive to known life, hence the blink. Range is ootentially unlimited, but calculations get horrifically inaccurate pretty fast, so standard travel is a series of short hops. Effective speed is limited by how fast calculations are completed and drive charge time. The former dominates long distance travel speeds and the former dominates short distance travel times. And yes, sometimes 'hyperbeings' hitch a ride back to our universe.

2) What is commerce like? I find this plays a bigger role in shaping the feel of a setting than even political and military setups. How fast does new technology spread? Are there large economic disparities between regions? What sort of economic regions even exist? How does commerce and economics drive politics and policy? How does commerce spread cultures throughout the setting?

3) What are the dominant cultures (which are more robust and tend to dominate local cultures when introduced, e.g. western culture dominating local cultures worldwide resulting in loss of local cultures)? How does this affect local animosities and prejudices? How does this affect politics? How does this affect protectionism vs. openness in trade and customs laws? How does this affect immigration, visas, etc. (important for world-hopping heros!)?