Learn Hardcore Russian: Друзья часто приходят в гости.

Because друзья is the subject of the sentence – the ones performing the action приходят. Subjects in Russian take the nominative case, and here we’re talking about multiple friends, hence plural.

What tense and aspect is приходят, and why is the imperfective used?

приходят is present tense, imperfective aspect of приходить. The imperfective is used for habitual or repeated actions (friends often come). A perfective form (e.g. приходят — they will come in future) would imply a single, completed event, not a recurring one.

What does the phrase в гости mean, and why is it used instead of a simple verb like “visit”?

в гости is a fixed expression meaning “to come over/to visit.” Literally it’s в + accusative, indicating movement toward being someone’s guest. Russian often uses this structure rather than a single verb.

Which case is гости in в гости, and why?

It’s accusative plural. After в to express motion toward something, Russian takes the accusative case. So гости here is the plural accusative of гость.

Why not just say друзья приходят without в гости?

друзья приходят by itself means “friends are coming,” but it doesn’t specify to where or to do what. Adding в гости clarifies that they come to visit (your place).

Can I use different verbs like идут or ходят instead of приходят?

Yes, but each carries nuance. идут literally means “are going (on foot)” and focuses on the act of going. ходят в гости (imperfective of ходить) also means “go to visit” habitually. приходят в гости emphasizes arrival at the host’s place.

How flexible is the position of часто in the sentence?

Fairly flexible. You can say:

Друзья часто приходят в гости.
Часто друзья приходят в гости.
Друзья приходят в гости часто. The nuance slightly shifts (e.g. emphasis on frequency vs. on friends), but all are grammatically correct.

Where does the stress fall in друзья and гости?

In друзья́ the stress is on the second syllable (я́), and in гости́ the stress is on the second syllable (и́).

How would I say “My friends often come to visit me”?

You add a dative phrase for “me”: Мои друзья часто приходят ко мне в гости.