If you are going to attend Sabbath services tomorrow you will be in for a treat as it's Harvest- the church will be decorated with flowers and fruit, extra musical pieces, etc. In addition to the mid-day one there's also an evening service.
What is the small chapel like building...across the street from the Church of Ireland.
That was the Good Templars Hall (temperance group)- after they disbanded the property went back to Aghadowey House/Castle (was next to the Parish Church).
Was Coleraine its market town..?
Coleraine and Ballymoney although nearby Garvagh also had a market, etc.
Was the sole entity in the center of Aghadowey...the church...was there a manse..??...or did there exist a general store...and a blacksmith...and a pub and travelers hotel..??
Aghadowey Parish is a bit spread out and didn't have a centre as such (although the Parish Church is near the centre of it. In addition to St. Guaire's (church of Ireland) there was the Presbyterian Church, Catholic Chapel (in Mullahinch then the present one on what is now Cullycapple Rd.) but lots of other Presbyterian churches in the area (Killaig, Crossgar, Ringsend, Ballylintagh, Moneydig, etc.).
There were pubs (one across from Presbyterian Church), shops and blacksmiths (one across from Termperance hall) throughout the countryside but the main industry in Aghadowey was linen with bleachworks, mills, cottages for workers and the big houses owned by the gentry (all except for Aghadowey House survive).
The current Manse for Aghadowey Presbyterian Church dates from the 1950s- earlier ones at Flowerfield, Greenhill, etc.
The Rectory was St. Margaret's (which can be seen from Parish graveyard and is in Belgian-gothic style) and earlier Rectors lived at Blackheath House (the famous hymn-writer's Cecil Francis Alexander's husband grew up there- she wrote Once in Royal David's City, There is a Green Hill Far Away and All Creatures Great and Small).
There were no hotels in Aghadowey but Garvagh, Coleraine, Kilrea and Ballymoney did have some and some of the pubs (such as Blackhill where there's still a stone milestone) might have had rooms to let.