Not a difficult one, but a time consuming one.
You'll have to spend at least a few hours improving all of the skills to get them to full, even after reading all of the research books.
The most difficult one is the gunsmithing and mending skill as you can only interact with any of the gunsmithing tools during an active aroura, and mending requires a tremendous amount of cloth to reach level 5 (without taking account sewing kit and fishing tackle durability).
There is an ammunition workbench in Blackrock Prison which doesn't need an Aroura to use but the only milling machine is in Bleak Inlet, which requires an active Aroura to get to and use.
Most of this will just be acquired over time, you can also make your life slightly easier with the Fire Master feat (but you will need to light 1000 fires overall on your account) and the Book Smarts feat can give you that extra 10% benefit from research books (though you also need 250 in-game hours of total research).