I just bought the new Bajaj Dominar 400. When I got my bike the engine coolant level was almost half. After riding 200 plus Km the coolant level is just above the minimum marker and it has not lowered after that. I am planning a small trip around 300 km in this coming week after which it would be time for the first service. Do I need to refill the coolant before the journey or can I wait till the first service?
As long as the coolant does not drop below the minimum level, it will be fine.
Assuming this is a brand new bike, or the coolant was just changed, the cause of what you're describing is likely air in the system. When the fluid is drained air enters the system, and when it's refilled small pockets of air will remain in the system. In order to get them all out, you need to run the engine for a while. As the coolant circulates the air will rise to the top of the system and be pushed out into the reservoir. As the system cools and contracts, fresh coolant from the reservoir will be sucked in and the level in the reservoir goes down.
Again, if the level doesn't continue to drop and it's measuring above the minimum line when measured per the instructions in your owners manual, it will be fine. On the other hand, if it does continue to drop you need to find out where the coolant is going.