Let's review your questions:

- whether to use a raw, html or lang block,

The RAW block is the most universal solution. You may use there the lnaguage kye too as the code like this one:

<bx_text:_bx_contact_menu_item_title_system_contact />

It will be inserted as the translated part too.

- whether to use a single block for the whole page and place all the html/php codes inside or use many blocks and place each page section in its own block

It depends from the task and design. If you consider that there is no need to connect the page parts then it would be good to have several blocks.

The last 2 questions - as I answered above, you may use the langauge keyes directly in the RAW code.