Most of this is going to be in books and not on the internet but there are some decent internet sources.
Wiki isn't bad for a team by team search and sometimes stadium pictures.
Retrosheet is a great resource for any period.
The 1878 Season
Baseball History: 19th Century Baseball Some good background info.
1920 Minor League Baseball League Encyclopedia - Baseball-Reference.com
Starts with the NL but has a lot of good info on teams. This is very hard to find on baseball reference so I linked to 1920 you have to press previous years a few times to get to 1876!
League Operating Rules
This one is from LGO. A lot of info on rules over time. Some is very hard to implement in the game.
19th Century Baseball [Archive] - Baseball Fever
Forum for 19th century baseball discussion so interesting stuff here.
The Directory of Major League Years
Quick year links on retrosheet.
The Economic History of Major League Baseball | Economic History Services
Some economic history less specific but it is written by an economist rather than a historian which is a plus.
ORIGINAL BASEBALL RESEARCH
Several articles by a SABR guy some 19th century some not.