Just a few comments:
Officially, there is no position known as Maintenance Overseer.
The main five are
PO
Secretary
Service Overseer
Watchtower Study Overseer (has that been officially changed?)
Theocratic Ministry School Overseer
and add generic
Congregation Book Study Overseer.
As to approval of larger capital and maintenance expenditure approvals: only if paid out of an existing maintenance fund held by one or more congregations sharing one building. Many congregations vote to put a sum into it on a monthly basis, then there is no need to make a resolution each month for maintenance expenditures.
but...............extensive remodeling and replacement costs have to be resubmitted to the congregation for approval. I know there are congregation elders that think differently but this is the input I have had from many elders and accounts servants in the last few years. A BOE can manipulate and shove through a resolution though and lie about the details.
Where do special pioneers fit into this chart? I understand they report directly to headquarters or is it to the CO/DO now?