Knives! I cannot stress how important great knives are for the kitchen! I have 3 solid ones that I use almost daily. A general purpose Big Ass Chef's knife, a Santoku for cutting foods that love to stick to your knives (potatoes, onion, cheese etc), and a flexible "fillet" knife. Something that can bend a bit and work its way into small spaces. Again, I use these about every day.
Good advice so far except I would say stay away from rice if you're looking to eat healthy. Brown rice or wild rice can be decent enough for you but its basically flavorless calories so consider this when looking for something to smother your etouffee over.
I'll stress spices as many others have. Staying away from salt can be rough unless you add plenty of zest in other ways. Garlic, pepper flakes, lots of herbs, etc. Fresh herbs too. If you're looking to impress a special someone fresh herbs and some lemon zest seals that deal 110% of the time!
I would say don't spend too much money up front buying a ton of tools and gadgets. You might not like them even though WE use them all the time. Example, I don't like slow cookers and don't use them. I have a zester but you wont need one for a while... and you could just as easily use another tool for free.
For the food itself... Cauliflower was mentioned and I second that. Its not a perfect replacement for mashed potatoes BUT in a 50/50 blend you get all the flavor and half the calories of Mashed Potatoes. I've also, while vegan, boiled up some cauliflower, put it in a blender, and seasoned it to hell resulting in a strange "cauliflower soup" that you would know as Nacho Cheese! Trust me, its amazing and you should be jealous.
Eggs and lean meats really help keep the carbs down. Protein in general. So beans, lentils, quinoua.
Sautéing or roasting anything will usually bring out more flavor so consider that on basic/simple meals.
Think about what foods you like, WHY you like them, and see if you can re-work them in the kitchen. Healthier would obviously be better but even if you can just MAKE the dish itself thats a win. I'd stay away from frying all together and just accept that its not something you need in your life.
1 pan meals
The Oven is your Friend
So, 1 pan meals... things like gumbo, chili, stir fry, etc. Think of something that will be relatively easy to cook, cuts back on the number of dishes, and will LOOK amazing. Stir Fry is my go to but you can use things like fajitas or pasta as well. Boil the pasta VERY al dente so its still got some bite to it, drain, rinse pan, add oil to said pan, add veggies into pan to saute. Once the veggies are about halfway done I then add the pasta BACK into the pan, giving it a bit of a golden finish, then top it all off with sauce. This will warm up your sauce as well and the more veggies you add the healthier the dish.
The Oven: Picking sides or even a main course that you can simply "set it and forget it" is a wonderful thing. Tonight I made a pork loin roast (just something on sale at the grocery store) that was already marinated and seasoned. Instructions on the package itself advise about an hour so I cut up some onion slices to line the bottom of my roasting pan (you can also use things like garlic, carrots, rosemary, etc) then laid the pork atop its bed of flavor. While that did its thing in the oven I was able to prep some other stuff and start on the sides. Corn on cob is SUPAH easy, set it in room temp water then turn to boil... when it boils the corn is done. HOORAY! Then I par-boiled some green beens then sautéed them with onion and some ham (would normally use bacon but didn't have any). Add spices or butter to tastes and if you wanted a little something extra maybe a roll or biscuit....
Bam. Purdy meal. Delicious meal. Healthy meal. And honestly pretty cheap.
I LERV cooking and I could go on about it for days. I would suggest that you try some simple dishes you haven't cooked before OR take some of your favorite foods and try making them at home. Good Luck!