Par is similar but superiour to the fmt(1) command included in the
base system.
Par is a filter that copies its input to its output, changing all
white characters (except newlines) to spaces, and reformatting
each paragraph. Paragraphs are separated by protected, blank, and
bodiless lines (see the Terminology section for definitions), and
optionally delimited by indentation (see the d option in the Options
section).
Each output paragraph is generated from the corresponding input
paragraph as follows:
1) An optional prefix and/or suffix is removed from each input line.
2) The remainder is divided into words (separated by spaces).
3) The words are joined into lines to make an eye-pleasing paragraph.
4) The prefixes and suffixes are reattached.
If there are suffixes, spaces are inserted before them so that they
all end in the same column.
WWW: http://www.nicemice.net/par/
set fo+=2
and maybe
set fo+=a
You must still manually add two spaces indent to the first line, but after that the rest of the paragraph aligns as you want.
You could probably make some mappings to automatically enter the two spaces. Maybe:
inoremap <CR><CR> <CR><CR><Space><Space>
or
inoremap <CR><CR> <CR><CR><C-T>
And similar for pressing 'o' in normal mode. Consider buffer-local mappings so it only happens for plaintext files.