If your child needs consistency, have some "safe" spaces where everything stays exactly as it is during any other time of the year. Your child's room is a great start. Additionally, we keep the bathroom, kitchen and playroom also free from decorations since he needs to access these rooms frequently throughout the day and we don't want to cause him any additional stress.
When extended family members come to visit, I know that our son doesn't recognize them. We try to remind family members that he probably will not want to come and say "Hi" or give a hug, and that needs to be okay with them.We also remind them that he may not show interest in staying around us to visit.
Sometimes, during the holidays, we want to go and do a special outing as a family or with friends. We like going to the pumpkin patch, drive to look at the lights and decorations on houses, and the infamous "Santa visit." For our son, we incorporate strategies like going on a "slow" day/time, maybe a Tuesday morning instead of a Saturday afternoon? If we are going with friends, we may also take him to visit the place we are going a day before so he can become more comfortable with the environment without a crowd.
No matter what our plans, we always try to have a back up strategy (like having a family member available to take him home) in case he does get overwhelmed or frustrated.
Remember: A short successful visit or activity will always be better
than a longer stressful one!