When my cousin purchased our grandfather's house he had the brick chimney removed, a small home built in the 1930's or so. He actually removed it himself along with a crew of his friends from the chimney outside through the walk up (by stair case) attic down to through the main floor to the basement and did gain that space it took up.

I'm not sure what the purpose of the chimney was (some type of heating I'm sure) there was no fireplace ever. There was typical HVAC system for as long as I can remember (40+years) sitting next to the chimney. I do think the HVAC vent may have been piped through the chimney to utilize the existing hole in roof/chimney.

They did have to cover the hole that remained with plywood and roofing material for short term. Short term because he had whole new roof/trusses put on the next year to make walk up attic into a living space and to be up to code to add dormers.

He said the job to remove the brick was tedious, took two weekends with some friends and family helping, mostly amateurs with hammers, pry bars, chisels etc. The chimney was not supporting the house in any way. It may not be a bad idea to have a structural engineer look at your plans. Check to be sure if you need a permit to do that however, you may want to check with your county.

I would get someone up there to stop water intrusion while deciding what to do. Even if just covering with a tarp and some duct tape and a bunch of caulking to keep any more water from coming in and doing anymore damage.

Be careful of covering it, in case it has vents in it, that need to be vented. They should be re routed elsewhere, before you cover the chimney, or remove it.

The chimney may need to be dealt with, but I wouldn't think it to be the source of water in the light fixture. In what condition is the roof and flashing? Might you have had ice dams or gutter issues that caused water intrusion at the eaves?

The roof is almost new… we had it redone in September 2019. I don’t know much about intrusion at the eaves as the roof is super steep/scary, so maybe we need the gutters cleaned or looked at?

Old central chimneys are often structural supports to the roof. If its in bad condition, your roof flashing may have pulled free and allowed water into the home. And the roof support can be compromised. You need an expert who understands old house builds.

So should we be looking for a plumber, electrician, roofer, general contractor? Thanks for the advice; this is our first home and we live in a small town, so we are a little overwhelmed trying to figure out who to call!

I would start with a quality roofer experienced in older homes.