I learned recently and I am about to finish a megillah on time or purim i’yh. The halachos I used Mishnas Hasofer and Otzar Sta”m [3 vol.]. I think that Otzar Stam is much more clear, while Mishnas Hasofer discusses everything.
To learn the umnos I learned from a sofer in lakewood who writes and taught me one and one. It is best to learn one and one then with a group especially for shapiras ha’osios. If youb are willing to come into lakewood I am sure my melamed will be happy to teach you.