I am comfortable playing with either. In games that have both I regularly switch between first and third person. As for windowed / fullscreen I prefer fullscreen if it will be a lengthy gaming session otherwise it is too much of a commitment.

To play, normally, fullscreen.

But by default, the first time it is launched in windowed mode.

Many games have weird resolutions or sometimes don't work right at first, if you force the first run in full screen mode and something doesn't go as it should, then it's a problem to exit the game.

A good and easy option menu. And if you can toggle it with alt-enter.

About first or third person, it depends a lot on the type of game and control.

For example, if it will be a doom type, that is, you aim and shoot, first person is better because the character takes away your vision area.

If it will be focused on melee combat or if it will have platform components, that is, it will interact a lot with the environment, better third view.

This is obviously my personal opinion, the best thing, if you can, is to implement both modes and for each player to select the one that is most comfortable for them. But the rule will be to avoid things that are uncomfortable for the majority, for example, many people complain about the platform in first person, because it is not intuitive.

I always play in a window on my main computer, cause I do many other things all the time. And I always preferred 1st-person, it makes me feel like being right there.

I usually play every game in full screen

I run almost all of my programs either full-screen or maximized.  Games, web browsers, file browser, command prompt, even my music player.  I can only focus my attention on one program at a time anyway, so why waste screen space for something I am not using right that second?

Borderless windowed fullscreen.

The only reason to go old school fullscreen is demanding 3d graphics, and even those games run in borderless fullscreen nowadays.  It is just not necessary nor nice for  multitasking operating system to have exclusive Fullscreen by switching resolution.

Some engines like old renpy screw up on Desktop zoom. Resizing the window works fine, but if you use the fullscreen option,   it incorrectly zooms by 150% or whatever your Desktop zoom is.

3rd or 1st person depends on a lot of factors. If done right, both work. iirc skyrim would just scroll the view in till first and out till third. But other 3rd have the character walking more to the left side .

Windowed makes the most sense, especially initially because it leaves the taskbar available, but if the game is engaging then I do like to switch to Fullscreen. 

If your game is in the style of Skyrim or Fallout then First Person would be my preference for default view.

Full screened for me. However, if the game automatically upscales to close to full screen, I'll go with that. I did a game jam, where I failed to make it automatically upscale, so the big complaint was "can't read settings in tiny window, to find full screen, 1 star."