[Dismounted]

Originally Posted by turtile

I want to highly customize the design of the site preferably with CSS.

Then the upcoming vBulletin 4 will be very useful to you, as its design is based around semantic HTML, with CSS playing the largest role in styling.

Originally Posted by turtile

Is any PHP required in order to build a custom template?

No intimate knowledge PHP is required. Templates are HTML/CSS/JS only, with some variables and conditionals. The only "PHP knowledge" required is simple comparison-type expressions.

Originally Posted by turtile

Are there any guides for this type of modification?

That really depends on what you're trying to achieve.

Originally Posted by turtile

I also want to integrate Photopost as well. Is there anything special I would have to do other than customize the Photopost template as well?

Photopost is a vBulletin modification, and uses vBulletin templates. By customising the vBulletin styling (e.g. replacing images, etc.), these changes will show on the Photopost templates as well. However, if you want to change the layout of how Photopost will show things (for example), then of course you will need to modify their templates.

Originally Posted by turtile

If I do use my own template, will any of the modifications cause trouble?

You just need to make sure you retain all of the information you need on that template (e.g. variables).

Originally Posted by turtile

I'm mainly looking at an ad management program that allows me to place Google Ads next to text posts and allows members to view the site without ads after registering or for a certain time after registering. Which mod would be best for this type of advertisement?

This would simply require some template edits, and we can help you with that once you are licensed.