Recently, I have setup several WordPress websites for clients using purchased themes. I have mostly just used the tools that come with the themes, such as the included shortcodes, styles, etc.
(1) A task that normally I would accomplish using PHP and a database, how to do the same in WordPress? Such as taking a user input, doing a database lookup, and displaying results on a page.
(2) I want to do a completely customized page design. Should I start with an existing theme (basic theme, purchased theme, "naked" theme?) and build from there, or must I develop my own theme from scratch?
(3) I like the fact that many themes are already responsive (desktop, tablet, smartphone, etc.), how can I leverage that but still do my own completely custom design/layout?
(4) I want to start with an existing theme but do a lot of custom CSS.
I am hoping someone with experience doing these kind of things can steer me in the right direction. I don't want to hack a WordPress site to pieces, I want to use best practices.
Coming from developing in pure code, it is difficult for me to get used to all the menus and options. So that has been a bit of a challenge. I guess I basically need to understand how WordPress works, how to customize it, etc., beyond just being a point-and-click, drag-and-drop WordPress developer.
It also seems like for accomplishing any task, the go-to solution is always to look for an existing plug-in before doing any programming. But there must be cases where writing your own code is the better way to go.
I am not looking for specific instruction on how to do the above items necessarily, but perhaps articles, online tutorials, a book, etc., for someone who is in my position? There must be others like me out there.