Getting enough sleep is the best place to start. That means sleep. Not just lying around being lazy. When you are rested, you will have more energy and not crave the high calorie junk food. Think of food not so much as something that tastes good, but as fuel for your body. You wouldn't knowingly put bad gas in your car, so why put bad fuel in your body? Be proud of good food choices.
As for lifting exercises, focus on your legs and back along with your core.
For motivation, you could think of yourself as a good example to the public you are helping.
I think the best thing to do when getting started is to actually schedule your workout into your day. Put it on your calendar with a time and place. Also have your workout planned out before you start. If you wait until you are at the gym to pick a workout you are much more likely to go the easy route.
You can do it, getting started is the hardest part! Don't let yourself give up!
You gotta take little steps and not let setbacks feel like complete defeat. Its difficult to change everything at once but we all have a tendency to set our expectations too high with fitness goals. We know we shouldn't eat junk so it becomes an all-or-nothing goal and when we fail we completely give up and eat more junk with this attitude like "what's the use, I obviously can't do it"
Take small steps. Three to seven minute workouts. A ten minute walk every day or every other day. Cut out one junk food or food group at a time. Eat a fruit and some whole grains at breakfast. Yogurt with granola & fruit is awesome. Eat one vegetable as a snack per day...like cucumber or carrot is simple. There was a period of my life where I wanted to cut out eating convenience store cookies in the afternoons when I got hungry, so I would buy a ton of fruit and say to myself I could eat as much as I wanted as long as I was eating fruit and not cookies. Stuff like that works for me, limits with no limits. I ended up eating a lot of fruit which some may say it was too much fruit sugar but really it was a good change for my quality of life. Switch to eventually only drinking water as a beverage, with black coffee or unsweetened tea. Liquid calories are a huge contributer to the obesity crisis.
Small simple.progressive changes are way more likely to succeed for implementing a real life change.
You can do this. There is absolutely no real reason why you can't. You are not some one in a million special case who just CAN'T get healthy with some simple life changes. You just gotta keep getting back on it when you fall off.