An Arkansas contractor taking work in Indiana deals with the same four questions everywhere: who licenses the trade, when a licence is actually required, when workers compensation kicks in, and where the business registers. Below is Indiana's answer to each, with the agency's own link.
Licensing
Indiana Professional Licensing Agency (Indiana Plumbing Commission)
No statewide general-contractor, electrician, or HVAC license; those are regulated locally. Plumbing is the state-licensed construction trade, via the Indiana Plumbing Commission under the Professional Licensing Agency (IC 25-28.5).
Workers compensation
Worker's Compensation Board of Indiana
Every employer under IC 22-3 must insure its workers' compensation liability or prove financial ability to pay claims directly; no minimum employee count; IRS-guideline independent contractors excluded.
Business registration
Indiana Secretary of State (INBiz one-stop portal, with DOR and DWD)
Tax registration
Indiana Department of Revenue
https://www.in.gov/dor/business-tax/register-a-new-business/
New hire reporting
We could not confirm a new hire reporting site.
Most states require newly hired employees to be reported within a short window of their start date.