This is for anyone who is starting to host tournaments. Start with a 1 table tournament. That is pretty doable to start, but after you have done a few, you will find ways to improve, or at least things that need to be improved. Typical number of players is 8, 9, or 10. They are not the same. While I've hosted several with one table of 11, I eventually decided to stop because it creates several issues I won't take time to go into.
Then go to a 2-table tournament. It's really hard to say how much more work is involved in a 2-table tournament, but it is way more work than a 1-table tournament. When you have mastered the 2-table tournament, only then would I try a 3-table tournament. When I did have a table of 11, it was because I was doing 2 tables of 10 and 21 showed up.
Once I felt very comfortable with 2 tables, I went to 3. That is the limit of tables my house could hold on one floor. What I immediately found was 3 tables was 2-3 times the work of two tables. Since I never tried more than 3 tables, I can't really say how much more work 4 tables is, but I would not be surprised if it was 2-3 times more work than 3 tables.
When I did have 3 tables, I was very dependent on other reliable people who could help -- at least one person per table. Even with 2 tables you need someone helping. I did play in the 3-table tournaments I hosted, but I remember thinking if I had another table, playing would be very difficult.
When you are talking 40 players, you are talking 4-5 tables. If you haven't master smaller tournaments, that is going to be very difficult. It's not easy even if you've mastered a 3-table tournament.
Getting good blind schedules and times is important too, but it's only part of the equation. It may be the easy part if you know what you are doing or listen to someone who does know what they are doing.
Does your 4-hour time include breaks, or is it playing time only? I planned 4-hour playing time tournaments. It's a science, but with 20 minute blinds, they ran 3:20+ to up to 4:20. So if you have a hard stop time, you need to get that figured out. Anyway, good luck.