The best way to sail a long distance race is with a team of people. Preferably on opposite sides of the globe so there will always be at least one sailor awake. But if you do insist on sailing a long distance race all alone, there is no real need to deprive yourself for sleep.

The boat will sail just as fast off line as it does online. And if you place your waypoints carefully, it will not run aground and even round the marks correctly.

The first leg of a race is usually upwind. If you simply place the 1st waypoint near the next buoy, there is no way of telling where the boat will sail. If it will tack to port or starboard and sail a long stretch or if it stay near to the direct line. Very likely the latter, but you stil have to be very careful that the auto navigation will not steer it too close to land or shallow waters.

Either use the autonav by wind option or place and extra waypoint to stay clear.

In this image you can see how I placed 2 additional waypoints (the top ones) to stay clear of the island. The top one is to stay clear in case the autonav dicides to approach from the south. The 2nd is to make sure the boat will stay clear of scotch point. Apparently there is also a Taylor rock, but the map doesn't have enough detail to make that rock a threat.

The 3rd waypoint is placed just outside the mark. You really have to be careful here. If your waypoint is too close or even on the other side, your boat may not round the mark in the correct direction and the passing will not be registered.

If the island weren't there and this would simply be the upwind mark in a big open ocean. You would still have needed the extra waypoint north of the mark to make sure the one near the mark would not be approached from the south. Because in that case you might still miss the mark.

Here's another example of how to place waypoints around a mark in such a way that you can be very sure that the boat will round the mark correctly.

There is nothing worse than sailing a race for days and then find out it reached the finish while you were asleep and it never crossed the line officially.
To prevent this from happening, place the destination marker not on or near the finish line, but beyond it. And just in case the boat sails towards it from the north or south and still misses the line, place an extra waypoint just in front or on the line.

The easiest way to make sure the boat stays on track is to set the autonavigation to sail towards the waypoint automatically. However, this is not always the safest way or the most efficient. When beating upwind, it may steer the boat towards a shallow area or towards land.

And when you expect a change in the wind direction, you may want to deliberately sail a certain course for a while. In those cases, it may be better to use the option to maintain the same angle to the wind. When the wind starts to shift, the boat will steer with it.

And just in case: Do make sure you have enabled your boat for offline sailing in the main menu. (Esc -> Options -> Gameplay)