Depends on the speed, but .7m/s^2 is a typical acceleration for trains. Cars can accelerate faster, and some trains can as well.
I just redid the math - to get to 300 km/h needs 4.8km, not 10 that I thought. Faster speeds need more distance or course. Hills also impact the distance needed. You also need to account for same safety distance for a lot of acceleration applications.
The distance to achieve top speed is irrelevant, it is the time lost that matters.
How much time is added to the journey for a single stop (including time for the stop itself, braking and acceleration).
Depends on what you are doing. If you are building track, then distance is what matters. If you are spacing trains out for safety both distance and time matters. If you are planning a schedule time is what matters (unless you are mixing local and express service on one track - see the safety sentence before). If you are planning track than you need to start with ideal schedule and iterate around the rest until you find something that actually works for all considerations.
There just isn't that much grip between the rails and the train, and any change to increase the amount of grip would probably sacrifice the efficiency and maximum speed advantages of rail. Remember, we're talking about steel on steel contact, which has incredibly low rolling resistance losses but is not exactly high friction.
With trains its expected that you can stand up and walk around at any time (or in some cases even have standing passengers), which does limit your reasonable maximum acceleration somewhat compared to modes of transport where your passengers are all seated and wearing seatbelts.
Why is that? Cars and airplanes accelerate much faster, without any real rider discomfort. If it's due to train hardware itself, wouldn't an assist to get the train up to speed work, in a fraction of that distance?