Regarding getting to Milngavie, there are also trains from both Glasgow Central and Glasgow Queen Street Stations. These take about 30 minutes.
Re. accomodation in Milngavie: There are 2 Premier Inns (Milngavie and Bearsden) which are within easy walking distance of the start. Both will be completely full of runners.
Re flying: Please note that there are 2 Glasgow Airports. Glasgow International Airport is a lot closer to Glasgow (15 minutes on bus to City Centre). Glasgow Prestwick Airport is a 45 minute train journey to Glasgow City Centre (the train station is right at the airport, so not too much hassle).