May a candidate appoint himself or herself as campaign treasurer and sign campaign checks?

Yes. Only the treasurer and deputy campaign treasurer may sign campaign checks. (Florida Statutes 106.021(1)(c)

1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.