1. I own a beginner level camera Nikon D3200 with 18-55mm lens. I just learned the aperture, ISO, and speed shutter. I need some pointers to study with my camera without buying any speed shutters, or camera lens upgrade because I'm saving up for an enthusiast level camera. What else can I do with my camera and lens? I can photograph like this (see photo) but I can't photograph trail lights or turn the water into silk.
(no trail lights)
2. I only have a limited budget, but I'm rooting for D7200. Is this a good practice camera who wants to take photography to the next level?
3. If ever I bought this camera, how much would more should I spend for camera accessories like camera lens, speed shutters, etc. I want to try every aspect of photography.
IMO you are selling short your current camera. The baseline Nikon's and Canon's are cameras which offer image quality equal to far more expensive cameras from either company. I would strongly discourage you from placing your confidence in a more expensive camera as an upgrade to your photographic skills.
Make the step to a more expensive camera only after you have exhausted the full potential of what you presently use.
Learn your D3200 to the fullest extent of your ability.
The feature sets offered with the D3200 and the more expensive Nikons are typically very similar. How you access any individual feature is a matter of the more expensive camera possessing more buttons you must learn and master.
I think, if you look carefully, you will see the D3200 has virtually every commonly used feature found on the D7200. Those few features not included on the lower prices camera are not "commonly used" by the vast majority of photographers. Their exclusion, therefore, means little to the student photographer.
How you access a feature is a tiny bit more difficult with the D3200 since many features will be found by scrolling through the functions list and the menus. This is hardly a bad thing for a student photographer.
Scrolling and observing will provide you time to actually consider the shot you are about to take. You will learn how to make decisions which will affect the quality and impact of your photograph. It will also make you more familiar with the less often used features of the camera.
Your better first move would be to acquire better lenses for the D3200 IMO. Until you own a few lenses to select from, the skills of a photographer are seen in how they figure out how to make do with the equipment they have in hand.
You can seldom go wrong with a faster and sharper prime lens vs the kit lens which was included in the D3200 package. A 50 mm prime is a safe bet with your camera and will up your keeper rate by increasing the precision of the D3200.
A single 50 mm prime lens is also far less money spent than buying a D7200.
You also seem to be confusing camera tricks with learning photography.
Concentrate on the basics of producing good photographs people want to look at.
What other photographers do is not what you should be aiming for right now. Learn how to take a shot of a stationary object that has good composition. Develop your skill at taking a photo of a human being which captures the essence of that person's inner being. Focus your attention and your camera on the person's eyes and tell a story with your camera. The story of human life as captured by your camera is infinitely more interesting and has far more lasting value as a record of their being than are tail light trails.
Your best bet is to take a photographic course and stick with the lesson plan offered. Free, on line education is available if you are on a budget.
Read your owner's manual several times to embed the data into your actions with the camera. If photography is about having fun with technology, then you do not want to be frustrated by a lack of knowledge regarding the technology.
Then simply take photos often. The more you use your camera, the more comfortable you will become with its functions and features and the more you will search for those ideas that are uniquely your own.