This is from the demo site:
[gallery columns="4" include="1186,1187,1188,1189,1190,1191,1192,1193,1194,1195,1196,1197,1198,1199,1200,1201" link="file"]
http://codex.wordpress.org/Gallery_Shortcode
The gallery shortcode is a WordPress defalut does not accept the same parameters as the portfolio shortcode which I created for the theme. You’ll have to reference the WP Codex for the settings (things like image_ratio="1:1" won’t work)
You don’t have to worry about the “thumbnail” size issue. The theme doesn’t use those preset WP image size settings. They’re configured for convenience (and so WP doesn’t squawk at me for not doing it) but the images for all areas of the site such as blogs, portfolio, image shortcodes, etc. are generated dynamically as needed. They still use the internal WP image resize functions but not the preset WP image sizes (thumbnail, medium, large, full). Considering you have the option to set the image size for almost every area of the site and have the be different for each and every instance of the blog, portfolio, etc. it would not be practical to keep a custom image size or use this native WP size naming method. You’re safe there. Set the thumbnail size to anything you need. (turn that frown upside down 
)
1. You can alter the spacing with some Custom CSS like what is below in your “Default Design Settings”
.gallery dl.gallery-item {
margin-top: 0 !important;
margin-bottom: 0.5em !important;
}
2. Thicker? It shouldn’t be. Did you edit any styles or CSS? If you want to change it you can follow the same method as described above but with this code:
.gallery dl.gallery-item .gallery-icon a {
padding: 3px;
}
3. Add the parameter link="file" to your shortcode. This is shown in the example copied from the demo site above.
