A non-shomer Shabbat Jew may not be a sofer.

A woman may not be a sofer. Even though women are obligated in the commandments of megila, they may not be sofrot for megilot nor for the Prophets (nevi'im) section of the Torah.
 

For Women and Sofer, see Sofer: Woman.

A mezuza (pl., mezuzot) is a small, sofer-inscribed parchment scroll containing the two Torah paragraphs commanding us to put mezuzot on our doorposts and gates: Deuteronomy/Devarim 6:4-9 and 11:13-21 (these are the first two paragraphs of the shema prayer.)  Each doorway that is related to where people live must have a mezuza.

Mezuzot are placed on the right side of doorways as you enter in apartments, buildings, or even recreational vehicles that you rent for 30 days or more (or that you purchase/own), in which you sleep.

A mezuza has protective value in that it reminds us to think about God each time we walk past a doorway or gateway, and so the particular name of God written on the mezuza (shin-daled-yud) likewise can serve as an acronym for God's role as “Shomer dirot Yisrael”—Watcher over the dwelling places of Israel.  

It is customary to check tefilin twice in each seven year period. Tefilin do not usually require checking, but you should periodically check:

• Tefilin of the type that can become pasul (due to white-washed parchment).
• Tefilin that are moved a lot, such as from place to place where there are large changes in temperature.
• Tefilin in humid climates, such as Florida.

NOTE Ask a sofer for advice about any of these cases.

You may not do “expert” or “professional” work of certain types on chol ha'moed, and some types of expert craftsmen/women may not do their trades on chol ha'moed.
Examples

• You may sew or lay bricks or other such labors, but not if you are an expert or professional in those fields and you are doing expert work.
• Skilled writers and artists may not do their professional writing, calligraphy, or drawing (even for free!) on chol ha'moed. They may not do calligraphy or sofer work (Torah, tefilin, mezuza), but they may write normally.
• If you are not a professional writer or expert craftsman/artist, you may write on chol ha'moed but the preferred practice is to use a shinu'i --an altered method of writing, such as:
  • Using your other hand,
  • Holding the pen/pencil differently from normal, or 
  • Writing diagonally across the paper.

Writing a Torah scroll (sefer Torah) is a mitzva but is not a priority; there are other activities that have a higher priority for Jewish observance.

A siyum can be held anytime a book of Torah or Talmud or any other holy book (sefer kodesh) has been studied for a long time; three months or longer is a good guideline. Simply reading through a book does not qualify; you must study it and understand it.