As for multi-table tournaments some necessary advices from members are given in this link: https://www.cardschat.com/forum/tournament-poker-59/how-you-play-tournements-many-players-272584/
P.s: If you are a beginner, it is better to start with a sit & go, with max players 6 and 9, the main thing in multi-table tournament with many players is to keep experience and patience, because such tournaments will be about 10 hours normally.
I love playing multi table tournaments but try to limit myself on how many I play because of the amount of time it takes to win one. I think you can be just as profitable playing 6max or 9handed sit n gos
I used to love playing MTT's but the above poster is correct in saying patience is key as they do last a while and my problem now is i get frustrated in very long MTT's and make plays i shouldn't have done otherwise.