Most English Churches of the 1640’s would have been of medieval date. They tend to sit in the middle of their associated grave yards - so you should have some open space and grave stones scattered around your church building. (In the UK separate grave yards located away from chapels/churches are more associated with later, so called none conformist faiths like Methodism – or they are post industrial revolution burial grounds created because many medieval church yards were full. Their effects would not have been seen until after the ECW).
The graveyard was usually encircled by some sort of ‘barrier’ but this was simply to delineate sacred ground for burial purposes, rather than signify some sort of physical barrier (after all, God’s House is supposed to be open to all…). So it need not be an imposing structure, and if I recall my old archaeology training correctly, most rural village churches in the Middle Ages probably had no wall at all – probably just a low earth bank demarking where the church yard began. By Tudor and Stuart times those wealthy churches with a bit of money to spend and a statement to make probably began building stone/brick walls around their churchyards (so much nicer than that old earth bank or that dilapidated wooden fence don’t you think?) but again these were just demarcation barriers and were often quite low structures (only waist or as low as knee height).
However, having said all that, a few ECW churches would certainly have made for a formidable defensive position in military terms. Especially those built on slightly raised ground, or some low promontory at one end of the village. Because of the higher elevation these churches often DO have quite high walls surrounding their church yards, which acted (in part) as an earth retaining wall. A defender standing inside the church yard might be looking out over a wall no more than waist height, but a potential attacker below him might be looking up at the top of the same wall a foot or two above his head!
As for the overall look of English churches – well styles vary from region to region, but for a good generic building the 28mm Hovels church is OK. The spire is a bit continental, but it would pass...
For something quintessentially English something like this would be better –
but sadly Hovels only do this in 15mm