Was the impeachment trial of Andrew Johnson a "media circus"?
Yes, the trial could absolutely be described as a "media circus"!
Johnson's impeachment hearings in the United States Senate were separated by a ten-day recess which lasted from 16-26 May 1868. You can probably imagine the furore in the press after the first vote on 16 May 1868 failed to reach the required two-thirds majority by just a single vote.
Examples you might find of interest about this aspect of the trial are the article 'Irresponsible Executive Power', published in Harper's Weekly on 16 May 1868 (i.e. before the result of the first vote was known), and articles published about the trial in the same paper a week later (especially, perhaps, Impeachment and the New York "Tribune" on p322)
The fact that the trial became what we would now describe as a "media circus" can be seen from even a cursory review of the contemporary newspapers. This was the event that forced the U.S. Senate to introduce a ticket system for seats in the gallery (a system that continues today). Demand for those tickets far outstripped the available supply.
United States Senate website
The United States Senate website has a section titled: The Impeachment of Andrew Johnson (1868) President of the United States which also has links to many useful and fascinating details about the impeachment.
Coverage in the newspapers of the day fuelled the public interest in the trials (after all, this was the first time that Congress was attempting to impeach a President!). The events were covered in detail, and the 'illustrated papers' of the day sent teams of artists to Washington in order to capture the key moments of the historic proceedings.
An example of this can be seen in the illustration depicting "The Audience in the Galleries Applauding at the Close of Manager Bingham's Speech", published in Frank Leslie's Illustrated Newspaper, from the U.S. Senate Collection (cat.no. 38.00365.001)
While many contemporary newspapers are only available from libraries or on subscription websites (like Newspapers.com), the complete issues of Harper's Weekly for 1868 are available on Internet Archive (they also have other volumes). These are fairly representative of the kind of media coverage the trial attracted.
As an example, in the edition published on 18 April 1868, under a headline The Impeachment Trial, they reported that:
"... the most lovely as well as the most distinguished ladies of Washington have been in daily attendance"
As you observe in your question, in addition to being a subject of national interest, the trial had also become a social event - a place to see and be seen.
(Other contemporary newspapers are available to view for free on Google Newspapers, although the search facilities there leave a great deal to be desired!)
Senate Gallery Passes
The public interest in Johnson's trial was such that the Senate was forced to issue gallery passes for the first time in its history. As the US Senate website notes:
For each trial day, 1,000 tickets were printed, allowing admission for a single day. Social and political protocol dictated the distribution of tickets, with 40 going to the diplomatic corps, 20 to the president, 4 to each senator, 4 to the Chief Justice, and 2 to each representative, with the few remaining tickets to be distributed to the public. Members of Congress received hundreds of requests each day for the highly coveted tickets.
If you are interested, the U.S. Senate site also has a collection of images showing many of the gallery passes that were issued for each day of the process.
Click to enlarge
Given the public interest, and the fact that the tickets were so heavily over-subscribed, it is perhaps unsurprising that some enterprising individuals sought to sell their tickets on for a profit. Those unable to get tickets directly from Members of Congress would just have to buy them at a premium if they wanted to be allowed to attend the sessions.