Take a No 56 bus to Exeter St Davids rail station. (On Sundays it's service 379 that you need). The journey takes 30 minutes. Timetable here:
http://www.stagecoachbus.com/timetables/563791 10309web.pdf
From there, take a train to Torquay. Some services are direct, others require a change at Newton Abbot. Journey times are between 35 and 45 minutes. (If the train calls at Torre, a couple of minutes before Torquay, you could get off there as the distance to St Marychurch is much the same but you'd find it much easier to get a taxi, if necessary, from Torquay).
For alternative travel options (e.g. by bus alone) use the route planner here:
http://www.travelinesw.com/cms/index.xhtml
For accommodation listings, see here:
http://www.englishriviera.co.uk/site/accommoda tion/torquay
For reviews, see here:
http://www.tripadvisor.com/Hotels-g186259-Torq uay_English_Riviera_Devon_England-Hotels.html
(Note that the link goes to the first of several pages of reviews for
hotels. Click the 'B&Bs/Inns' tab, near the top of the page for further listings).
Chris