Yes, it has been reported that when you get the invite to order you can delay. The tri motor is likely to be very late 2027 or in 2028 as a 2029 model year.
Probably. No-one knows how long Rivian is going to honor reservations (year(s)), but most likely for a good long while so they can fill them. I would think once their Normal 100% capacity comes online and production capacity >= orders, reservations wouldn't matter except on holding price.
What do you mean by "reserve"? If you put down $100 now, you are not locked into any configuration.
If you've been invited to start the purchase process, then you have to put down an additional $400 non-refundable, but you can pick any configuration currently listed on the web site, even the configurations that aren't shipping yet.
But the tri-motor variant has not even been announced yet. You can't select that configuration because it's not something that Rivian has committed to. So if it does come it could be years from now, or it could be never at all.
If you want to gamble on a tri-motor being available when you need it, go right ahead But don't blame Rivian if you lose that bet - they're not promising anything about a tri-motor right now.
There is no harm in making a $100 reservation, but in all likelihood by the time the tri-motor is available the reservation pool will be exhausted and they will just be directly taking orders.
