Is it okay to use a 5x Barlow lens with a 100mm Orion Skyscanner Telescope

I'm referring to the telescope shown in the picture at the link below:

http://www.telescope.com/Telescopes/Dobsonian-Telescopes/Mini-Dobsonians/Orion-SkyScanner-100mm-TableTop-Reflector-Telescope/pc/1/c/12/sc/28/p/9541.uts

I want to upgrade this telescope to the highest maximum quality, not just in terms of magnification, but in most aspects if not all aspects. A few of these aspects would be ease of use, stability, and eye strain. I would like to analyze and consider costs vs. benefits, but I do not know what they are as I have no previous experience in astronomy. Consequently, I'm relying on advanced amateur astronomers here for this information. Which of the following lens would be best to increase the aspects mentioned above and why?

Orion Shorty 1.25" 2x Barlow Lens
Orion Shorty-Plus 2x 3-Element Barlow Lens
Orion Tri-Mag 1.25" 3x Barlow Lens
Orion HighLight 1.25" 3x 5-Element Barlow Lens
Orion HighLight 1.25" 5x 5-Element Barlow Lens

Recently, I observed an interesting bright spot on the moon, but I'd like to get a closer view of it and am enjoying myself so far. Astronomy seems like my thing. All help is greatly appreciated!

You're right -- too much magnification will not improve the image. Generally, 50x per inch of aperture is considered a good amount, as much more will just begin to get blurry because of diffraction issues.

So, in the end, perhaps the best would be a good eyepiece with enough eye-relief to make it easy to use.

This telescope has a 400 mm primary mirror focal length. Magnification of a given eyepiece can be found by dividing the objective focal length by the eyepiece focal length (20 mm eyepiece = 20 x,
10 mm eyepiece = 40 x).

A single additional eyepiece of focal length 5 mm or so would give you magnification of about 80x, and 2.5 mm eyepiece would give you about 160x. Often the 2.5 mm eyepiece would not give you a better image than the 5 mm, unless viewing conditions were ideal.