I'm pretty familar with phpbb, I'll make a few suggestions.
Since it's a new install there is two simple things you can do right now to make your life a whole lot easier.
First for the image attachment mod go here, it's probably the single biggest mod and the most complicated to install EXCEPT when you do it on a clean install which you have.

Also the most popular for obvious reasons. :
http://www.phpbb.com/phpBB/viewtopic.php?t=74505
After you download the zip file from the page uncompress it and look in the docs folder for the instructions on installing with pre-modified files. Since you have a unmodified version of phpbb you can use this. There's a link in that document for downloading the additional modified phpbb files. It's simply a matter of uploading the attacment mod files and overwriting your existing phpbb files with the additional pre-modified ones. Run the database file and you'll be able to attach images and files to your posts.
The second thing to do is install Easy Mod. If there is one thing you should do is install this even if it's just used to install phpbb updates. It's the simplest and easiest way to make phpbb modifications.
http://www.phpbb.com/phpBB/viewtopic.php?t=217673
Once you install that most mods can be applied using it. Last thing to note is that some mods have a database update script you need to run seperately. Read the instructions for each to insure you install it correctly if you install any. There's literally thousands of modifications you can make to phpbb....
Most can be found here:
http://www.phpbb.com/phpBB/viewforum.php?f=15
On a final note... if you use a theme other than the default one you can run into trouble since the mods are made for the default theme. It won't screw anything up but they won't be available in the other themes in a lot of cases. You can however modify the default theme quite easily. Use the admin control panel to modify the colors and other attributes. You can further customize it by modifying the templates. Look in templates/subsilver/... specifically the overall_header.tpl . The TPL files contain the HTML that produces what you see on a page.
As always backup often if you start messing with stuff... don't be afraid as that's half the fun with phpbb.
