Help needed with site idea – is it possible and how?

i have installed wordpress 3.0.1 on a test server and it all seems to be running fine. the help i need is more to do with the site design and if its actually possible to do.

basically i have been asked to ‘sort out’ a non-profit online magizine website. currently the only way we can update our site is by re-coding the page to contain a new article, and use ftp to upload it to our web host. the site has now reached a point where it needs an upgrade and i think wordpress is the way to go! i have a good technical knowledge but webdesign and coding are a bit beyond my capabilities, but here is what i would like

the main homepage needs to have a logon script, which can verify registered users from a database. i also need a way of adding new users and basic user admin that can be performed (much like the forum login on this site) currently i do not have a database of users, so this would need to be created from scratch.

i also need a banner/button bar that has links to the facebook, twitter, stumbleupon, youtube, myspace and digg. all these accounts already exist.

from then i would like a nice drop down menu that links to the various topics. i need to be able to change the content of the menus fairly easily, as this is done a few times a year.

i would like a photo streamer, which displays a selection of photos from within a catagory or folder. currently, the images are saved on my hosting server in an image folder, but i can uploadthem to flickr or another service.

the main content of the page needs to have 10 boxes, each of which show an article from their respective catagory.

also on the main page i would like a twitter widget, that will display the last 3 or 4 tweets from the twitter account.

as well as all this, i have to have the logo and banner adverts. the website relies on sponsers paying to advertise on the site, which covers the running costs.

to give you an idea, the origional website is here
: https://fameonline.co.uk/

the styling of the website can change, but it will need to be consistant throughout.

from the admin side, i need to have 2 admin account, one for myself and one for the main editor of the magazine.below that i need some sort of seniour contributor account, that can edit any posts made on the website, and below that i need contributor accounts, that can post articles to whatever section they are writing for (ideally i would like them to only be able to access their section) and that the articles are saved and wait for seniour contributor/admin approval before being posted. there are multiple contributor accounts that wont always be used by one person )i.e. differnt people write different articles for a section). articles are currently written once a week, but only published once a month. i would like to have it change to articles being published as and when they are written.

my main question is can all of this be done? the current sire is such a mess im not even sure where to begin! currently the site is written in PHP and uses CSS style sheets and various scripts. i was thinking to give the site a consistent look i could use the existing CSS styles. i would need someone to be very kind in pointing me in the right direction for what to do. im doing this website as a favour to the magizine (its a friend who runs it) so im not making any money from this! anyone who gives me a lot of help can be credited on the site.

i should mention that at this stage, the functionality is more important then the looks. at a real basic level i want my current website on my wordpress server, using wordpress to publish articles. once that is done the graphics and styling can be changed