Well done on getting back to the site and making another go at weight loss. Sometimes you just have to keep at it even in the face of past failures to get where you want to go.
Unfortunately, there doesn't seem to be any magic balance of macronutrients that works for everyone. I've known people that were successful on low-fat, and I've known people that were successful on low-carb. Probably the one thing that these people shared in common was that they threw out all the processed trash in their diets and started eating real food, like salads, minimally-processed meats (no sausages, ground-up "mystery" meat, spam, etc.), fresh-squeezed juices, and cooked cereal grains other than rice like barley and quinoa. You'll feel loads better just by eating real food for a couple days. As for the right ratios, you'll have to figure them out by trial and error.
For exercising at your current weight, you just want to get moving, above and beyond what you do at work. How far is the nursery from home? Is it possible to walk there? At the gym, the rowing machine and elliptical are low-impact cardio activities that will help you burn off calories without stressing out your joints. Swimming does this also. Finally, I'd toss in some free weight lifting to supplement. With your build (as you described) you should be able to handle a decent amount of weight, so try doing some barbell curls or bench pressing to start out. Even if you start off just using a naked bar, you'll train a lot of supporting muscles, up your metabolism noticeably, and, best of all, these movements will carry over to your nursery job. When you get more comfortable with the bar and improve your muscle/fat distribution a little you can even move on to slightly more advanced exercises like squats and overhead pressing.
As for motivation, I don't really know what to tell you. You could keep coming back to this thread and I (and am sure other cool guys here) will try to keep your spirits up. Something that's always motivated me is going for bigger numbers in the gym. Whether that was more distance on the rowing machine, or bigger lifts, I concentrated on improving those numbers and lost a lot fat in the process. Out of curiosity, are you a gamer? Because a lot of my friends, as well as myself, got motivated to exercise more and eat healthier after they made the connection to..... "leveling up."