Would anyone be able to link some primary documents they would recommend? And I'm having some trouble both online and in libraries trying to find who all was at the treaty signing; where would I look to find all the diplomats and government officials involved? I cannot read Russian or Japanese unfortunately, but the paper is mostly centered around certain American aspects of the event.
If anyone could help (or if there is a subreddit more suited to these recommendations) I would greatly appreciate it! My project spanning the entirety of this semester is a make-or-break for history majors and I will take any help through additional sources I can get.
This is some way outside my area of expertise, but I can at least give you some pointers.
The first place I would look for English language primary source material on something like this would be the relevant volume of Papers Relating to the Foreign Relations of the United States, more commonly known as FRUS. It is, as the title implies, the official record of the US State Department, documenting important negotiations and events in which US diplomats have been involved. In this case, the 1905 volume contains diplomatic correspondence covering US coordination efforts in the run-up to and aftermath of the negotiations as well as American neutrality vis-à-vis Russia and vis-à-vìs Japan. Dig around and you might find other sections of interest as well. If nothing else, some the published telegrams will provide you with the names of the members of the Russian and Japanese delegations.
For secondary literature a quick google scholar search reveals that Dartmouth College held a centenary conference on the Treaty of Portsmouth, some of the papers from which were afterwards published in an edited volume. I'm not familiar with the work, but being well credentialed it may well be worth asking your local library if it can get hold of a copy. The references and bibliography contained within should also give you pointers for further reading.