Orlando is my home station and I usually start my travels from there. Even though not required, I go up to the ticket window and make sure everything is in order. I do not check baggage and I normally pick up my tickets in advance, so it is not necessary - but I am bit neurotic, so I check in. If you need special assistance, I would certainly check in.
Depending on the weather, I either sit outside or inside while waiting for the train.
Normally, the station attendants will make announcements as to where to stand in order to board the train. The coach passengers line up towards the rear of the train (if the sleepers are in front) which will be to the left when you go out the station doors looking at the tracks. If there are large numbers of passengers boarding, which is the case on most summer days, they will have the coach passengers line up by destination. Boarding the train is often slow. They will try to put families together, but it does not always happen.
The sleeper passengers will board towards the front of the train (to the right when you exit the station). On the Silver Meteor, there are usually 3 sleeper cars and you will board the car to which you are ticketed (9810, 9811 or 9812). Boarding the sleeper cars is much quicker than coaches because there are fewer passengers in the sleepers.
Sorry for the long answer to a short question.