RFA would not have howitzers which were handled by Royal Garrison Artillery on the whole, but something a little smaller. A sergeant would most likely lead a detachment [not a team, which was the horses] of 6 to 8 men handling the loading, laying, firing and maintenance of an 18-pounder under the direction of a junior officer as section commander, within a battery, within a brigade.
Have you looked at the Long Long Trail website - click on the Royal Artillery bit on the left side of its opening page. There's lots there.
<http://www.1914-1918.net/>
Afterthought: RFA DID have howitzers after a shake-up in mid war, but in more general terms you should think of the 18-pdr field gun.