I'm surprised your vet didn't go over that with you at your appointment.

Feeding soft food is ok if your baby is having a bit of a problem wanting to eat anything. Nuke the food just a bit to get it good and stinky as cats sometimes won't eat what they can't smell, and a stuffed up nose doesn't make for good sniffing power. How old is the kitty? If he's older than 6 months it's ok to feed the adult food just for now while he's sick. Younger than 6 months I'd stick with kitten canned food if you go that route.

It's possible to carry the virus on your clothes. To be on the safe side have a pair of coveralls or pull on sweats over your clothes, and slippers for your feet, for when you go in the sick kitties room, then shuck them when you go out. And yes, wash your hands good, lathering for a minimum of a full count of 30 seconds with antibacterial soap. Don't share bowls or litterboxes between sick/healthy cats. When the kitty is no longer sick you can disinfect the bowl/litterpan with bleach, then wash in HOT soapy water and resume using it again with other pets.

If symptoms aren't at least improving over the next 3-5 days you need to call your vet. It may take a week or two for Jax to be feeling normal again.

I'm unsure of how long they are contagious, I think that depends on the virus suspected, your vet is the best one to answer that question.

If symptoms get worse (not knowing how bad your kitty already is) ie; bloody nasal discharge, refusing food even goodies, lethargic, not using litterbox, or not going at all, neglecting to groom, vomiting (more than once), difficulty breathing/wheezing, open mouth breathing, drooling, or thick green or yellow nasal discharge, then get your kitty to the vet again.