My first time playing D&D. I’m starting with the default equipment my class gives me (I’m a rogue), so my question is: how much money would I have? I know I can roll 4d4 and buy the equipment and I did that but ended up with 54 gp. Is this too much? If so please explain how I do this.
There are exactly two ways to determine starting equipment.
Starting Equipment
Take the starting equipment listed in your class, and the starting equipment listed in your background. The latter will detail how much (not much) gold you’ll start with.
Starting Gold
This is the method you described, taken from PHB p. 143 – You roll 3 to 5 1d4’s and multiply it by 10gp, with the number depending on your class (Monks also don’t multiply it, since they don’t need starting weapons or armor). Obviously, this roll should be done with your GM present.
Which option is superior? That’s ultimately up to you and how much you like randomness. Keep in mind that some GMs may disallow one method or the other, and in fact, the latter method isn’t allowed under Adventurers League rules (though I hear you may sell and buy equipment before your first adventure but that’s another question).