Microwedding/destination Wedding Invitations

You should plan for the number of people that you have invited because you won’t know how many people will come until everyone has RSVPd.
You could ask to RSVP as soon as possible and people should know in advance since they’ll have to make travel plans.
I’m in a similar situation. We live on the west coast and 95% of guests live on the east coast or in Europe. We have had a lot of people already make their travel plans (were getting married in December) but we still don’t know whether we’ll have 145 people (number we invited) or 100 so we’re just planning and saving expecting that everyone will be there.

Also, I think January is way too early to have people RSVP like you said between work and needing to save up for travel, I think that super early. I wouldn’t do before March unless your venue needs counts earlier. You just need to find a venue that holds all people invited.

It's rude to ask people to RSVP early. Everyone would love to know numbers as early as possible, but as a host you need to give your guests a reasonable RSVP date, which is about 3-4 weeks out from the wedding, or 1 week before your venue needs final numbers. For planning purposes you need to make sure that you can host everyone you invite just in case you have 100% acceptance rate (it does happen, even if it's not likely). In your case, find a venue that can physically hold at least 70 people. Tell your caterer that you're inviting 70 but that you estimate ~35-50 people attending (e.g.). Make sure you have the budget to feed all 70, just in case.

Definitely stick with and plan for the larger number of guests. No harm, no foul if the number of guests decrease. I think January is too early to RSVP for sure. You can also ask your caterers when they require a final headcount. Personally, I'm setting the RSVP deadline a month before the actual RSVP deadline just in case I have to hunt down stragglers.

You will want to find a space that can accommodate the number of people that you are inviting. In order to give everyone enough time to plan, I would send save the dates. Invitations don't normally go out until 8-6 weeks prior to the deadline with the RSVP date a week or two before your final headcount is due to your caterer so that you have time to follow up with guests who forgot to RSVP. Sending out invitations too early and having an early RSVP deadline can result in problems with guests not knowing if they can actually attend which could mean you end up with a lot of guests not replying or having to change their response last minute.

I think you can ask for RSVPs really early, but I wouldn't just because it's likely not to be accurate. Lots of people will think "i'll say yes just so there's a spot if we do go, and then end up not going," so then your count won't really mean much. I'd plan for the largest number possible (i.e. everyone you're inviting) and then worst case, you have more space. Really, given the current climate, that isn't a bad thing!