it’s really not that hard. i’ve done it for several years, for various candidates & part units.
The keys are keeping accurate records (so you know where all the money came from, and where it was spent) and reporting that carefully. And I’ve generally found the staff of the reporting agency to be quite helpful when you have q question.
Many years ago, IIRC it was the writers’ union (??) in India that protested a particular government policy by running almost every member in some ridings. The ballots ended up being several pages long, very confusing and very disruptive. The government responded by jacking up the filing fees for the next election.
Canada had a similar situation with the Rhino party, that ran in several elections in the 1980’s as a mockery protest against elections that were a foregone conclusion. They had a platform that included steps like scratch-and-sniff unemployment cheques, changing the name of Ottawa to Miami Beach to improve the weather. The government, having no sense of humour, has now made the filing fee for federal elections about $1500 to discourage this.
(There was also an episode where some unknown crank filed papers to lead the conservative party. Everyone thought “why would he?” until the convention. He made an awful rambling speech, but the party leaders realized too late the guy had bought 20 minutes of national prime-time air time (the convention was televised) for a mere $5,000 - a bargain even back then. Now, IIRC, filing fees for leadership hopefuls are around $40,000.
I assume the filing process is similar for congress; you gather signatures from X constituents of the district, and present that nomination form with a filing fee to the returning officer who places you on the ballot. To get the party endorsement, I assume the party’s selection if there is a contest requires a similar filing with the party in time for the primaries.
IIRC, Obama helped secure his senate nomination by challenging the validity of his rival’s nomination form. The other guy had not double-checked the names on his form for validity, too many were disqualified so he did not have the minimum for valid nomination form. Allegedly this is a frequent tactic in Illinois.