Are there any sources for state level base maps to build my custom maps on?
Most maps I see have a base map of the state with roads, lakes, rivers.... Are any of these available for download?
Individual states may have their own data available. But you could also use data from OpenStreetMap shapefiles:
https://wiki.openstreetmap.org/wiki/Shapefiles
There are shapefiles from USGS and USFS for landcover, transport, buildings, hydrography etc
Right. You can go to the National Map, zoom in on your area of interest and choose the type of data you want. If you are interested in a specific US state, next to "area of interest", choose "selectable polygon" from the dropdown, then choose "US State of Territory" from the other dropdown. Now you can click the state you want and limit your search to it.
https://apps.nationalmap.gov/downloader/#/
Thanks for the information. Lots of stuff for me o look at.