For racing spacecraft, you'll need to focus on conservation of delta-V (total available change in velocity, AKA: Total engine burn-time multiplied by acceleration) to allow for course-corrections (because space is big, and there's a lot of crap in space that can cause solar-windage and drift off-course). An interesting bit of physics is to pretty much power-dive at a planet at full-burn to improve delta-V (as you are shedding mass while gaining momentum) and aerobraking to cheaply bleed excess velocity so you don't land at your target-window like a bird from a windex-commercial.
Also, a lot of things can kill your delta-V rating, stowaways, particle-buildups,
engine damage/malfunction, and propellant-leak to name a few. Oh, and collisions hitting stuff at nearly the speed of light is bad... like, one kiloton of TNT of impact for every gram that hits you.
This said, about 90% of your ship's mass will be propellant, not living quarters, and not structural components,
just propellant. Your ship will accelerate exactly ten times better when empty than full.
The other issue is acceleration, as you may need to change your velocity 'quickly', and by that,
I mean precisely and if you cut the burn too soon, or start too late, you'll crash and die like someone who took a second too long to turn the wheel during a powerslide into a rail.