The only RPG I know that is/was really good that had more than 100 levels was Maplestory (ow the nostalgia).
It had the design of different levels in each class though (job advancements) which gave you only a few skills and unlocked more when you advanced to the next job. That way, you didnt get an overload of skills to learn when you reach level 10/8.
But in the end, it is just the matter of what you use the level variable for.
Ofcourse you use it to have an indication of the strength of your character and it is a bit of a progress showcase thingy, but if you take a look at different RPGs, you can see that the differences when leveling up matter and how much/strong those differences are.
After that, you have the level cap.
No level cap is kinda bad imho, so you would have to cap it at some point. (Also to avoid game crashing moments.)
And you dont want to spend a few decades to level to the max, especcially if the actual interesting gameplay starts at max level.
To start of, just use something normal like 70 to 150 as level cap. You can change it later on anyway if you change your mind.