A thought may have crossed your mind: is there a max level for my characters? And the answer is not well known, not even by google.

The answer is yes. And either you're gonna do years of grinding, or you can just press Win + R, type %appdata% when prompted, open MMFApplications, click your save (fnafw1, 2, or 3, depending on which one you chose), then typing the following:
1lv=99999
2lv=99999
3lv=99999
4lv=99999
5lv=99999
6lv=99999
7lv=99999
8lv=99999
9lv=99999
10lv=99999
11lv=99999
12lv=99999
13lv=99999
14lv=99999
15lv=99999
16lv=99999
17lv=99999
18lv=99999
19lv=99999
20lv=99999
21lv=99999
22lv=99999
23lv=99999
24lv=99999
25lv=99999
26lv=99999
27lv=99999
28lv=99999
29lv=99999
30lv=99999
31lv=99999
32lv=99999
33lv=99999
34lv=99999
35lv=99999
36lv=99999
37lv=99999
38lv=99999
39lv=99999
40lv=99999
41lv=99999
42lv=99999
43lv=99999
44lv=99999
45lv=99999
46lv=99999
47lv=99999
48lv=99999
this will automatically set them all to one hundred thousand, or 100000, the max level.

oh, and if you don't have all the characters, type:
1have=1
2have=1
3have=1
4have=1
5have=1
6have=1
7have=1
8have=1
9have=1
10have=1
11have=1
12have=1
13have=1
14have=1
15have=1
16have=1
17have=1
18have=1
19have=1
20have=1
21have=1
22have=1
23have=1
24have=1
25have=1
26have=1
27have=1
28have=1
29have=1
30have=1
31have=1
32have=1
33have=1
34have=1
35have=1
36have=1
37have=1
38have=1
39have=1
40have=1
41have=1
42have=1
43have=1
44have=1
45have=1
46have=1
47have=1
48have=1

this is the most efficient speedrun strat why has no one used this