I used to fly there a lot in twins. Firstly never get the Shawbury weather as much of an indication of what Welshpool has!
The surface winds will be different as will the cloud bases.
Welshpool has its own microclimate
Shawbury giving overcast 200 will usually mean Welshpool will be 700!! Fog at Shawbury will often have Welshpool clear and visa versa with the river and valley making for localised fog and mist.
There is an unofficial approach but do not do it unless you are very familiar with the terrain as the hills come very close! The Runways are 22 04 the approach on the radials used for GPS as 210 and 030 which keep you away from the hills! Overlay that using the dme ndb and preferably a Radar altimeter.
As for how low you can come ??? Officially the MSA and certainly the MSA if you do not know the area like the back of your hand.
Pace