How old are you, do you have any health problems and have you done a lot of exercise in the past?
Will the 5km run be outside up a hill? 5km in 30 minutes is doable at a steady pace and the sit ups etc are achievable in a day but not necessarily all in one go.
The trick is to be steady and consistent, not go flat out, that will only discourage you.
This is an excellent plan to get to running 5km - and will work if you stick to it
https://www.nhs.uk/live-well/exercise/running-and-aerobic-exercises/get-running-with-couch-to-5k/
It is essential that you don't run every day, rest is just as important especially in the early weeks. It is too easy to fatigue yourself and burn out. That leaves you feeling that you can't do and that is when people give up.
On the days you don't run, stretching exercises are good and you can incorporate the squats and sit ups in to that - but again don't go mad. If it hurts, stop. Gentle stretching avoids injury. Walking will also increase your stamina on rest days without putting strain on your muscles and joints.
Drink plenty of water, eat well and get a good sleep routine. It all helps.
You have plenty of time to achieve your goal by March, doing it steadily and avoiding over exertion.