Questions about exporting: subtitle, level formating, custom highlight markers error

[Xiha <xiha@laposte.net>]

Hello,

I am writing a paper-like document in Org-mode, and experimenting with 
export to HTML and PDF (via LaTeX) in order to share drafts. Not sure 
yet what the final formatting will be. I am quite new to Emacs/Org-mode, 
know little about css and nothing about LaTeX. Using Emacs 24.5.1 and 
Org-mode 8.2.10 that came with it.

1) I would like the exported document to have a subtitle under the title 
in a smaller and/or lighter font. The latter requirement makes splitting 
the title with a newline not quite a solution. I believe I saw 
discussion somewhere about a #+SUBTITLE keyword for LaTeX or HTML export 
(as opposed to Texinfo which the manual says is supported?) But that 
seemed to be a feature-in-progress? What is the status of this? Is there 
an alternative I can use for now?

2) I have #+OPTIONS: H:9 num:9 because explicit level structure is 
important for this document. I would like to have more control over how 
this is exported, e.g. by setting heading font size as well as 
left-margin widths per level, for a staircase-like effect similar to 
that obtained with org-indent-mode in Org itself. (How) can this be done?

3) I forget through which command/menu, but I set custom markers that 
'highlight' the words they surround, within Org itself. I'm using the 
'leuven' theme which makes them stand out with a yellow background - 
useful for passages that need work etc. But now when I try to export to 
HTML or PDF, it fails with "Unknown marker at 10497". Is there a way to 
get the highlighting in the exported document? Alternatively, can I tell 
the exporter to ignore the custom markers, i.e. treat them as regular 
characters?

Thanks in advance.