I started with your challenge April 2 (because I'm no April Fool ) and fairly quickly escalated to 4 sets daily of 10 pushups/situps/scissors kicks and added 320 "flutter" kicks daily (80/set x 4 sets) except for a 5 day vacation mid-April when those numbers were about 50%. However, I've more than made up for the slackitude in the last 7-8 days. Hopefully, this routine is now a habit as I've worked through some shoulder and groin soreness and can comfortably knock out 5-6 sets of each on a daily basis now and hope to continue indefinitely.
I *think* you could easily add 50-100 situps daily over the next week or two as you're a young, healthy, handsome and fearless fella.