Difference between lower and higher current rated ESCs and electric skateboard questions
Does the weight of the person riding the skateboard affect any of the parameters for the project?

Not the ones you have stated.  The cargo weight effects the acceleration at any fixed power setting.  It also effects the maximum speed you can go uphill at any fixed power setting.

Does an esc that is rated for 6S(24v) and 30A suffice?

You say the maximum operating point is 24 V and 23 A, so a 24 V and 30 A rating should suffice, if the specs you quoted really are the worst case.

Say my project requires a maximum of 30A (an example), whats the difference between if i use a 40A ESC and a 100A ESC?

Each should be able to handle the problem.  The higher power unit will likely be larger, heavier, more expensive, and possibly less efficient at low power levels.