Module development and code questions

I am just starting out in drupal and wondered how I get access to the user id for a person who is logged in.

I have date form field and a task name that I would like to insert into my mysql database.

My test insert statement is:

$query = "INSERT INTO qatask_task (task_name,start_sched) VALUES (\"$task_name\",\"$start_sched\")"

The fields from my form are assigned to variables before this (i.e $task_name = $form_values['task_name']) for ease of reading and requirements I have for this design.

I would like to extend the Voting Module to display voting criteria on mulitple axis for a particular type of node. It should also create an average score based on an aggregate calculation on all of the axis. I love the simplicity of the voting module and would like to extend the functionality to accomplish the above.

I had a developer create a custom classified ad functionality for my drupal site and upon looking at the work, there are a bunch of includes in the code and extra php files floating around in the root folder and the /includes folder. Should I try to integrate all the code into drupal so that it gets saved in the database, or should I not worry about them?

My concern is organization and long-term sanity.

I'm a real newb when it comes to drupal, but I have some experience with PHP and SQL, so it's not all foreign. That said, I want to create a block for my site that will announce when users have a birthday coming up. I've seen a few of this type module for 4.6, but nothing that works for 4.7

It's nice that Drupal has a forum built-in, but it's not exactly what I want for my site. It doesn't really *look* like a forum. So, basically, my question is: What would I need to do if I wanted to change the template and things? Also, would I need to redo my edits each time I upgrade my Drupal installation?

Thanks in advance!