Well, let‘s take a look at your situation. What level are your athletes or clients at? New athletes or clients probably would not benefit from percentages as much as more advanced clients, as they need to learn how to perform the lift correctly first and foremost. Second, a new client will adapt to the exercise so fast that by the next time you perform the exercise, their 1 rep max may be out of date and thus their percentages would be incorrect (if they used to bench 100lbs, but after 2 workouts they can bench 110lbs, that 60% you have them working out as now too low to cause the adaptation you are looking for).
A good starting point in your quest to make a home budget, is to take stock of your current and recent situation, and list out all your monthly outgoings. If you only do this from memory, there is a chance you will miss one or more important items. You probably have several sources of information on what those regular outgoings are, and whether they are easy to find depends on how well organised you are with your paperwork. It is worth checking back over at least three months bank and credit card statements, and jot down what your regular payments are out of those. At the same time, you can also make a note of items of expenditure that may recur later on.