What Software Do You Use To Create Your Sweetest Tumblr Themes?

I am not a web designer (which is why I love the simplicity of Tumblr) but I want to start a site for my work, an online portfolio, if you will. I am an architect (of buildings/space/furniture) with some very limited experience with code and scripting in modeling software and I set up this blog where I used to work (it hurts my eyes to look at it now!). So, I can sort of figure out how to tweak HTML and have done so with my own shits + giggles test Tumblr blog http://bonos.tumblr.com. I like the simplicity of that layout and would like to keep it generally the same (2 columns, white background, minimal) with some improvements as described below.

For my own work, I need to be able to control it more and have some navigation (tabs or links at the top or in the sidebar) to pages of significance (background, contact info, cv, projects, etc). I would also like the main content to be scrolling and transparent. The closest I have seen is this beauty Jam Factory.

Anyhow, I would like some help on this. How can I edit Tumblr HTML in a software package that makes sure my code is correct? Can show me WYSIWYG? Is Dreamweaver good for this? Which elements of the HTML do I need to keep/lose? Can I just cut + paste it into Dreamweaver (I have tried this and it seems not to work)?

Also, would like to add elements/widgets, whatever such as: calendar of entries, tags (or categories)...

Thanks so much in advance for any help.