The gourami likely died of stress. They are extremely fragile at best. The shrimp would have hated a brand new tank without any biofilm, which is what you gave them when you scrubbed it out with vinegar.
The other fish may have died of stress as well, but it is hard to say for certain. But unless there is some ghastly infection in a tank, that is killing everything, never scrub off the biofilm ! It's pretty essential for a lot of fish and very necessary for shrimp.
Most of the BB live in the filter. There are some in the gravel, a very few may be in the biofilm, but the vast majority live in the filter, which is where conditions are optimal for them. Flowing water, food and vast amounts of surface area to colonize. They need solid surfaces to stick to, to colonize.
The temperature is a bit higher than I'd keep it.. I aim for the lowest temp tolerated by the fish in the tank as a general rule.
Without testing there is no way to know if you started a cycle with the change, but even with the scrubbing and substrate change, a cycle should not have happened. Unless the filter was allowed to dry out or you changed all the media, it should have remained ok for the time it took to do what you did, and you kept it running in the bucket so it should have been fine.
A lot of people think BB live in gravel, but by and large this is not the case. Some do, but not that many. But other bacteria do live in substrates, and if they all died off at once, that might be enough to possibly trigger a spike, as if a fish had died and been allowed to decay.
One reason I keep Ghost shrimp is because they are such useful scavengers for things that die. Snails are also useful for cleaning up dead things, but usually they move in after the most of the meat has already been eaten. If I lose a large snail, the body will be cleaned out by shrimp in a surprisingly short time, and then the MTS will polish the remaining bits from the shell.