For GST, you can choose between a 5% rate (no/restricted ITC) or an 18% rate (full ITC). Regarding ITR-4, it is generally intended for presumptive income under specific sections (44AD, 44ADA, 44AE). Since Section 44AE applies only to goods carriages, passenger bus operators often do not qualify for ITR-4 and may need to file ITR-3. Please consult a tax professional to evaluate your specific eligibility.