Hi I surpose the most impotant question you asked is are there any dangers of buying a house next to a substaion,well substations are very safe but they can go bang and catch fire,if they overheat,I surpose it depends how big it is and how near it is to your house,in my street there is a house with a small one right next to there side entrance,I have to admit I would not want to live there,the other part of your question is that the electricity company own it.
Best Regards