We ended up doing a full-weekend party where people could drop by whenever they can. The first guests came on Friday around 6 pm and the last ones left on Sunday at 11 pm. In the end people were spread out evenly. Some came with kids in the day, others alone in the evening. This way there was really time to sit down and talk with old friends whom I hadn't seen in years or even decades.
For food, we ended up having ingredients in the fridge for a few quick foods like Vietnamese rice paper rolls, and we'd make it together with new guests if they were hungry. It worked out fine.
Of course dedicating the entire weekend to a party is a big commitment, but I think it actually reduced the level of stress compared to trying to do a traditional "dense" party on Saturday night.