Hi purpler, what you need here is custom template fields, that are known in MODx as Template Variables (TV). Here is a quick example:
1)
Go to Elements > Manage Elements > Template Variables > New Template Variable
Template Variable Name: box-01
Caption: Box Content
Input Type: Textarea (Here you can choose also RichText, which is TinyMCE or FCK)
Template Access: Here select the template you’re using in your home page.
2)
Repeat step one and create box-02 and box-03
3)
Open your template and add the Template Variables that you have just created like in this example:
<div class="box">
<h3>Rođendani</h3>
<p>
[*box-01*]
<br />
<a class="readmore" href="address" title="Pročitajte više">Pročitajte više</a>
</p>
</div>
About your second question, you are correct. Your template could look something like this:
[*content*]
[*box-01*]
[*box-02*]
[*box-03*]
[*content2*]
[*content2*] is just another Template Variable with Input Type: RichText.