Solved I want to upgrade either Movie Studio 14 or Vegas Pro 14. Thus I have some questions...

Thank You, if you can answer all or some of these questions!
And of course, any constructive suggestions and/or opinions are welcome!

For my Real Estate clients, I make 1080 Photo slideshows, which I post to my YouTube channel.
Movie Studio Plat has always had an easy way to set this up.
I usually choose 8 sec display time, with 2 sec fade. No other pans or zooms or special fades.
I then hand pan or zoom each image slowly, according to the direction of the door/room, or POI the next image has.
Nice pro effect. I add titles with the last century, default media generator.

I purchased Vegas Pro 14, with the hope of editing and rendering 4K video, and better control over the overall video look, like Lightroom for video.
I have 4k video (consumer grade) capability. Mavic Pro, Nikon DLSR.
I just presumed Vegas Pro would be better. Now, I'm not so sure.

1.) Is there a secret backdoor to find the Slideshow program in Vegas Pro 14 or 16? Or simple work around? It's found under INSERT menu in Movie Studio.

2.) Biggest question! So, does Movie Studio Plat 16, handle 4K editing, and rendering ? I will qualify this; "YouTube" 4K. LOL!
I have 4K monitor for Lightroom Raw image editing, and I can view "4K" video online.

3.) Will I be able to use some of my past Movie Studio 14 Suite, "extras", I have installed; ProDad Mercalli Plugins 4.0 / Newblue products / Boris products etc.?
I need a good Chroma Key program, also a semi easy, New Blue or similar "Basic" Titler would be nice. No need for top o' the line.

4.) As far as you can tell, what advantages are there to upgrade from Vegas Pro 14 to 16? VERSUS, Movie Studio suite 14 to 16. I can choose only one.
I can afford Movie Studio Suite 16 at this moment. I really haven't used Vegas Pro 14 much.
My only drawbacks with it are, supposedly no easy Slide Show maker, and the price point for what I will actually use.

Again thanks to the community for help in this.

Hi HawaiianEye

1.) Is there a secret backdoor to find the Slideshow program in Vegas Pro 14 or 16? Or simple work around? It's found under INSERT menu in Movie Studio.

The Slideshow creator is a Vegas Movie Studio feature only - it is primarily aimed at beginners and home users.
All Vegas Pro versions do not include the slideshow creator. It is assumed that pro level editors know how to create their own slideshow using the default tools.

2.) Biggest question! So, does Movie Studio Plat 16, handle 4K editing, and rendering ?

Yes, Vegas Movie Studio Platinum 16 and Vegas Pro, both support 4K video editing.

3.) Will I be able to use some of my past Movie Studio 14 Suite, "extras", I have installed; ProDad Mercalli Plugins 4.0 / Newblue products / Boris products etc.?

Yes and no. Some third party effects plugins that come packaged with different versions of Vegas Movie Studio or Vegas Pro, are locked to only work with the version of Vegas you bought the plugins came with. If you download and install the free trial for Vegas Movie Studio Platinum 16, you will discover which "extras" will work in v16. If they are compatible, they will automatically appear in the program.

The New Blue FX Chroma Key plugin that comes packaged with Vegas Movie Studio Suite 16, is a terrific green screen tool and works 500% better than the inbuilt Vegas Chroma Key plugin.

4.) As far as you can tell, what advantages are there to upgrade from Vegas Pro 14 to 16? VERSUS, Movie Studio suite 14 to 16.

Not everyone needs to use Vegas Pro. I know many business owners who are quite happy using only Vegas Movie Studio Platinum to make videos and slideshows. It's about using the right tool that works best for you.

Each user will have different features that are more important to their workflow. In my personal opinion, one of the main reasons I use Vegas Pro over Vegas Movie Studio, is so I can use the advanced Colour Correction tools in Vegas Pro, to achieve accurate colour levels.

I made a comparison video/article many years ago, that explains the major differences between Vegas Pro and Vegas Movie Studio Platinum here:
www.moviestudiozen.com/free-tutorials/sony-vegas-pro/512-sony-vegas-pro-12-vs-movie-studio-platinum-12

Regards
Derek