What do you mean by "a long term development plan for a piece of land underused at present"? I presume you are referring to land owned by the Council. If you want to explore all of the options for this, I suggest including as many brains as possible in the process would be worth considering, i.e. take it to full council.
There are few rules about terms of reference for committees, or even the need to have committees, so the council should adopt the structure that best meets its needs. Many councils set up a planning committee to respond to planning applications, as the deadlines invariably fall between the normal calendar of meetings. Whether you extend the remit of the planning committee to include planning policy is for you to determine locally. Do you have a Neighbourhood Plan or have you considered creating one?
Do you need a Finance Committee, or are you creating one because other councils have one? What functions will the FC undertake that could not reasonably be carried out at your regular meetings? Some councils are large enough or sufficiently complex in their affairs to warrant this, but many are not. If you Google (other search engines are available) "parish council finance committee terms of reference" you will see many examples of poorly considered finance committees. An FC comprising every member of the council? Random undefined spending powers. Several examples of an FC undertaking roles that are legally the responsibility of the RFO. Others that take on duties of the full council. Some have such broad powers that I wonder what the other members of the council are allowed to do.
It's always worth having the "why are we doing it like this?" discussion.
