Funeral/Death of Non-Jewish Loved One?

TLDR: My (not Jewish) former father-in-law took my side in my divorce years ago. Story for a different time, for anyone that would like to know more. Thus, I've remained close to his family.

One such family member just passed away a few days ago. This was an uncle through marriage — specifically, he was married to my FIL's sister, so his BIL, if I'm doing the genealogical math correctly. I was close to this gentleman — he was career military like my ex-husband, and his first wife passed away (many, many years ago) from the same medical condition I've had since childhood. Since he and his wife lived just one state south of us (at the time), they visited us regularly. Over time, he and I developed a close bond, and over time he took on more of a fatherly role to me, seeing me through the best and worst of times, often sharing with me incredible guidance and wisdom for life. Last week, he went out for his daily walk, took a fall, and hit his head, and that was it. I've been waiting days to hear more about funeral arrangements, and just today finally received an update. The funeral is scheduled in one month from now.

I have questions:

- This uncle wasn't Jewish. How do I honor him?

- The funeral is in a church. Am I allowed to attend?

- Are there any restrictions or rules I should be aware of?

Thank you in advance for any recommendations.