Chill out. You are too focused on what other people thing and not focused enough on the fact that the main event here is you making a huge emotional, legal, and financial commitment to another person. A venue that maxes out at 120 will seem plenty full with 80. Really.
Most people have weddings of less than 100 guests. Some are tiny. Very few people have the financial resources to spend enough money to have a huge wedding -- not to mention most people don't have that many close friends and relatives. You invite the people who you want to share this special day with -- not to fill out a room. It is also very normal to have about 10% regrets and 2% no-shows (people how can't make it at the last minute). The larger the group of people, the farther away they have to travel, and the less close they are to the bride and groom, the more likely they won't come. That means trying too add people who really couldn't care less about your wedding, probably isn't a good idea.
A reception is the couple's "thank you" to the guests for attending the ceremony. At a reception, if you provide a comfortable environment and refreshments -- you've done your job as a hostess. This is not a game night, a gala ball, or a night club. You and your fiancé are welcome to have any number of different types of "entertainment" if you want. Whether or not a guest has a good time is up to them -- not you.