Intend to sit for, to start with (7)
I believe the answer is:
propose
'intend' is the definition.
(I know that propose is a more specific form of intend)
'sit for to start with' is the wordplay.
'sit' becomes 'pose' (as in sitting for a painter).
'for' becomes 'pro' (as in being 'pro' or in favour of something).
'to start with' means one lot of letters go next to another.
'pose' after 'pro' is 'PROPOSE'.
'to' acts as a link.
(Other definitions for propose that I've seen before include "Present for consideration" , "advance" , "Put forward a plan" , "Put forward (an idea)" , "Pop the question" .)