Module development and code questions

I'm posting this in Module development because I think that's where it fits best, although my question is partly about Drupal in general. I'm trying to determine is Drupal was a good fit for a project I'm working on. I'm fairy sure the answer is "Yes Drupal is perfect for this" but I'd like to hear it from someone who actually knows Drupal :)

I have three requirements for the website:

1) A basic informational website with tabs and pages and links and all that stuff. No visitors will be able to edit pages or anything, just myself or other employees.

2) In that list of tabs will be one special tab, something like "My Account". This is where the bulk of the functionality of the website will be. When you hit this page, instead of displaying an article, it will run custom PHP code to access a SOAP server and display information, configuration forms, etc. For example something like /MyAccount/ will be the home for the user's account, which will list some details about their account in an editable form and have some links. /MyHome/ListMyProducts might list products they have purchased etc. ( I guess I'm saying I want to mostly use Drupal for my site but have a bit of a custom webapp inside of it ).

I think that I just use some sort of node hook and if the name of the node is one of my special pages I deal with it however I want. On the right track?

I'm trying to add support for the video_cck module, and I'm having trouble with checkboxes. This code, according to how I understand it, should set the checkbox as checked and then if it's unchecked on form submit, add a variable to the variable table in the database. It does neither of those. If I change it to a textbox, for instance, and enter some text, it works flawlessly. I'm thinking there's something I don't understand about checkboxes...
[code below]

I'd like to change a number of stylistic features for the comment module, mainly:

1. Add some help text
2. Change/remove the "Post new comment", "Your name:" text
3. Most importantly change the way the nested comments are outputted to make them truly "nested" like this wordpress plugin.

I've worked out how to do some of this with phptemplate_comment_wrapper and phptemplate_comment_form but it seems that I can't get around hacking the comment module for the rest.

OK, I'd like to dive into custom coding to make the most of Drupal. There are some modules that do almost what I want to do... So, I'm wondering how to modify their behaviour.

Let's get specific:

If I want to do Y (e.g. add 2 numbers and store the sum in DB), right after a module does X (e.g. child node created), where would my PHP code go?

Should I roll my own module with my new DB table set up in the installation file, and do some kind of hook alter on the other module that is doing X?

I've just started developing modules for Drupal and I've come across a problem I can't get around. In my module, I defined one menu item with a callback. This worked great for a while, and now I'm getting the Access Denied method every time I try to access this node.

My menu code is as follows:

I'm about to begin a site that will have some content that can be voted on. The idea is that when pieces receive enough votes they are promoted to the front page, or a dedicated page.

I've been playing around with most of the modules and just wondered if there is one in particular that folks would recommend.

Drupalit and vote up/down would seem to suit my needs. However, there's also fivestar and jrating.