As much as I hate to admit it- some of the best guides out there to study are government publications. Transport Canada put out TP10038-e in 2003, the small fishing vessel safety manual which I could consider as the baseline for the bare minimum seamanship considerations to be had onboard a vessel of any size. You could view this publication as a sort of primer for the watchkeeping mate curriculum; as all of the topics covered in this publication are studied in greater depth by watchkeepers. (also available offsite here)

Chartwork and pilotage level 2 is the highest level of chartwork certification available and is defined in page 167 of TP2293E. The syllabus covers definitions of earth's geometry, ability to plot courses on a chart accounting for wind and tide, practical position fixing, tidal calculations, and ability to use publications for passage planning. The most basic equipment needed for chartwork are a parallel ruler (or 2 large protractor triangles) and a navigation divider.

overall difficulty: 3/5
focus on: taking the time to learn chartwork properly without rushing work, light mathematics review

The navigation safety level 1 syllabus is laid out on page 171 of TP2293E, and covers the content of the collision regulations, principles of the STCW code, and recommendations from the international conference on training and certification of seafarers 1978 (or from any colregs textbook including these welcome additions).

overall difficulty: 4/5
focus on: reading the rules carefully and creating a system early on for note taking or memorization

Communications level 1 and 2 are in the process of being merged into one curriculum, but in TP2293E (page 47/8) are still split into 2 seperate small syllabuses. The content is use and recognition of international code flags, and other internationally recognized systems for communication in distress.

overall difficulty: 1/5
focus on: memorize flags and some associated morse, familiarize with publications beforehand

The syllabus for GSK level 3 is on page 173 of TP2293E. The content covered is largely publication based and the examination is open-book, allowing access to 22+ international and canadian publications.

EPS is a prerequisite for SEN-O or SEN-1, as part of the simulation training portion. EPS, like SEN, is issued by a training institute and is defined in a seperate publication than other courses, TP4958. This course is about the equipment used onboard for navigation and focuses on how it works, and the margins of error in all shipboard equipment and systems.

overall difficulty: 2/5
focus on: memorizing definitions. try to line the course up with SEN-O or another simulator course following afterwards, as sometimes it can take a long time to get into simulator courses in particular.