You get what you pay for is ever so true. I would never send any of my equipment to Precision camera repair or for that fact any general repair facility. They fix all kinds of cameras not just one specific brand of camera.I used to send a lot of work to Precision and they got so bad at attempting to fix cameras and lenses that were out of warranty that I stoped using them. Go to a reliable camera store and make sure that your equipment under warranty is sent back to the manufacturer for warr service, some times it takes a little longer that way but it gets done right and it also has a warranty on the repair.I can probably count on one hand the returns I had to do to a manufacturer for warranty repair service from the hundreds of camera repairs I handled for customers over years of service. Precision camera repair got so bad we had a direct dial button on our phone for problems with their repairs. Think of it like this would you take your car say a ford to a Nissan dealer for repair, I know I wouldn’t.
If I remember correctly Nikon made extension tubes and I think they made a tube with a helicoild so you could adjust the extension getting you to about 3x if not they have bellows that will do just that and still be able to use your flashes however the best I ever saw was a enlarger lens set up with a 105mm Nikkor enlarging lens which you could also use reversed, Nikon used to make a BR 2 reversing ring for their 55mm macro lens which might also work for you. Macro photography is very specialized and very special equipment. Good luck in your journey.
The way I always understood Nikon, the main reason tp buy Nikon is to use their glass. If something fails on a lens of Nikons you send it back to Nikon for repair because they have the expertise and equipment to repair it properly. The understanding I have is Nikon is the only authorized repair facility. If you have a problem then get in touch with their customer service dept, I understand that no one wants to be without their equipment for any length of time but have faith they are really good.
Great choice of bodies, the 7200 is a great camera body, don’t forget that it’s a DX body so wile choosing a lens your 1.5x factor comes into play. Now your widest 28mm is now 42mm and long end becomes 210mm. Best deal I have seen on 7200 body is a refurbished by Nikon for 709.00 at Adorama.Good luck on whatever your choose might be use it and have fun with it.
The reason your f stop changes as you zoom is the light passing thru your lens has to travel a longer distance to reach your sensor in the camera, the f stop size is not changing. If you have ever seen say a 70-200 2.8 lens you would notice a very large front and rear elements in that lens which allows more light to pass thru to sensor or film.If you have ever seen a view camera. A 210 mm lens is a 8 inch lens, you put a 360mm lens on which is a 14 inch lens the light has to travel 6 inches longer thus creating a exposure difference. The same works with every camera lens combination ever made. To determine your focal length in inches use 25.5 mm to the inch. Their are conversion charts available to convert the light falloff to f stops.I know this is a little complex but that is very basically how it all works.Better yet try using a true macro lens on your camera, focus at infinity on a fixed light source that doesn’t change, put your camera on S (shutter priority) now set your shutter speed some where in the middle range of your light source, now focus in to your closest and look thru your camera while focusing and you will see your f stops changing as the light has to travel a longer distance.