What do you need to do in order to start a new political party in Wisconsin
Develop a charter, bylaws, and other organizing principles.
File for a petition for a new 501(c)(3) group with the IRS. It would be prudent to avoid conservative principles like Constitutionalism, 1st Amendment rights, support for the rule of law, if you support Israel or Jews, support of religious liberty as the US Court of Appeal in DC has found that the IRS still as of Aug 2016 is targeting such groups.
Build a grassroots organization and support for initiatives, get funding
Get on the ballot! Wisconsin
The laws of Wisconsin provide two routes for creating a legally-recognized political party.
You can petition to have your party on the ballot (statute). The petition must be signed by 10,000 registered voters, to include at least 1,000 registered voters three different congressional districts. It must be submitted to the Wisconsin Government Accountability Board by April 1st.
Find the petition form here.
By Election Success
Your party will also be eligible to be on the ballot if, in the past election, one of your candidates for a statewide office received at least 1% of the votes cast (statute). To be clear - this means they ran as an independent or write-in candidate for a state office (Governor, state Senator, state Representative, or others) and received at least 1% of the votes in their district.
If this happens, you can request that the Wisconsin Government Accountability Board place your party on the ballot. Again, this must be done no later than April 1st.