I havent used RPG Maker, (I personally use Unity) but coding wise it should be fairly easy to implement, just make sure that your total max value for any stat (eg. hp, mp, strength) is calculated using the total sum of multiple variables, such as one that scales according to level (or location/checkpoint in your case; or heck, you can just have it scale with both, have one variable that scales with level and one with the location), and another that is a sum of that stat from your equipped items.