"I have lots of good memories."
Translation:יש לי הרבה זכרונות טובים.
The endings ים and ות are most of the time used on masculine and feminine nouns respectively. However, that does not mean they are the masculine plural and the feminine plural endings per se. זכרונות is a masculine word. זכרונים does not exist.
There are some theories that in very early forms of Hebrew (before any writing), the endings were not aligned with gender and instead represented some other meaning, for example, tangible versus intangible, but over time the endings were reinterpreted by speakers and became more standardised along gender lines, but not completely, and hence you still have some unusual cases like this one: זכרונות טובים.
I don't think that's true, either. המון is used the same way הרבה is, and the dictionaries seem to agree, for example -
We can’t be expected to know about and answer the hundreds of questions that come in on the forums. We are merely volunteers. The forums are meant to be a community where learners can help one another.
As for זיכרונות/זכרונות and ניצחונות/נצחונות, both forms are fine and in use.