For Grid Bot, you cannot add money to the running bots, the feature to add more investment is not implemented yet. But keep in mind, you can always run another bot with the same pair up to 30 per pair. You can utilize this by using your additional fund to run the 2nd bot, so you have 2 bots running. You can do this up to 30 bot in a pair.
There’s no such better thing or worse thing, both parameters can excel in its own way. If you want to know, you can run bot with same parameters but different grids number. Let it run for a couple of time and compare the result based on your strategy.