So.. I’m getting married October 17, 2020

If you are worried about infection then it would be fine to ask everyone attending to wear a mask. You should state this on the invite so people will be prepared. You should also provide hand sanitizer. I would also have some spare masks in case someone forgets. If someone refuses, they can decline the invitation. No one should be upset that you are thinking of everyone's health. The alternative is to have a small ceremony.

Depending on where you are, if may be enforced anyways. We actually just postponed from 10/17 to next year in upstate NY. I hope you get your day!

Our wedding is 10/10 - while we weren't sure masks would be required, we have opted to include custom masks (we're making ourselves) in our Welcome Bags. The masks will be optional unless it is still state mandated. Currently in the state of FL, masks are required if under a roof, however we will also be outdoors so it may not be required.

Currently our county requires them. Before then, I was going to strongly encourage and provide masks.

I think it would be a smart idea to at least recommend masks. If you're able to, I also suggest providing them or at least having a few available in case someone forgets theirs. You could also space out the reception tables, as well as ceremony seating, further apart than normal, limit the number of people per reception table, and have hand sanitizer available.

I would encourage people to wear them, especially if you have guests who are more susceptible. The majority of my family has some type of underlying health issue that makes them more susceptible to covid.
At this point, I would make sure you are following the guidelines for your state/locality and check with your venue to see what/if they are doing anything extra to meet those criteria.
In another thread, one of the ladies shared this link to amazon https://www.amazon.com/gp/product/b086wc1ldd/ref=ppx_yo_dt_b_search_asin_title?ie=utf8&psc=1 if you want to buy them in bulk for your guests:

We are giving our guests the option to bring their own mask If they want to wear one. We will be doing temperature checks as guests enter, and will supply plenty of soap at bathroom sinks, and hand sanitizer at every table.

We changed our reception venue to one that isn’t requiring/enforcing masks for everyone. Of course people can wear one (especially my grandma) but I personally wouldn’t want to go to a wedding where I had to wear a mask all night

Yes, please ask all of your guests to wear masks. If you make it optional, the people who don't wear them will be the same people who are not taking precautions in the rest of their lives, so they'll be more likely to have, and spread, the virus, even if they don't know they have it.

I would. As pp said if it’s optional, the likelihood is a lot won’t wear it

I personally wouldn’t want to attend a wedding where other guests wouldn’t be wearing them. I’d want it to be required.
Masks are mandatory in all public spaces in my state anyway and can only be removed while sitting at a table to eat or drink. I’m still super nervous about my friend’s November wedding though.