One easy way to get some information/planning tips - look at the websites of some Italian restaurants that host private events or catering companies - they will often have menus posted to give people an idea of the large party options - usually to show people what they can expect in their price bracket, but it could help you to see how many entrees/apps/sides/desserts that they recommend for groups.
Not enough information for anyone to give a well-thought out answer.
What you cook and how many different items depends upon the equipment you have (the ability to keep hot food hot and cold food cold, and get 2,3,4,5,6,etc, hot dishes to the buffet line at the same time all in excellent condition.) Are you cooking out of a small apartment with a 3 burner stove and a oven that struggles to keep temp or do you have a professional home kitchen with a 60" stove, 4 ovens, warming drawers, large refrigeration units, ice makers, etc?
All of this makes a world of difference since your menu is dictated by your equipment.
I've planned a lot of medium to large sized parties around this range and generally, at least 3 entrees, and 4 if you can do it. One entree should be entirely vegetarian. I would probably do beef, fish, chicken and vegetarian. This way the pescatarians also have a choice other than the veg, which is usually pasta, esp for an Italian dinner.
What's your budget for each event? Are you looking for a hands on approach, or are you going to put this out one, possibly with a back up tray of each. My experience is things with too much cheese will dry up of time, or more exactly, 30 minutes time. I also find seafood does not hold up well either. Last, what's your level of experience in the kitchen? Can you cook up 40-50 chicken breasts, cut in half and pounded with relative ease, or would this be a challenge?
For the summer event...I like the idea of cold seafood salads.
BTW.....are you doing these parties privately or commercially for profit?
1-meat, can be anything from lasagne to sausage and peppers
1-Veg, such as eggplant parm or rollatini
1-Fish or chicken. Chicken cacciatore or marsala are good buffet items
1-Hot pasta dish such as baked ziti
In the summer you can drop the hot pasta and sub a cold pasta salad.
When you have more people you shouldn't add additional selections, just more serving dishes of the same menu for ease. Either 2 different buffet tables or lines starting at either end of the same table.
BTW>>>many Italians don't conside, but Pasta a main course, but a course served before the main course.
I've been to loads of Italian get-togethers (showers, weddings and family birthdays) and I've always seen at least 4 main entrees: pasta, pasta, meat (chicken), meat (beef) and then maybe a combined like lasagna, plus salad, antipasta and the like. I'm not sure if this is any help...
(Maybe I just know a lot of big eaters!)