I'm slightly curious as to why you have to stay near Oxford to build your hours up after the ATPL. Have you got already something lined up for afterwards? If you read the fora regularly, you will know that it is far cheaper to do it elsewhere and will probably take you longer when you consider the bad weather compared to Florida etc. I did not go the self-improver route and am therefore just trying to give an unbiased, but perhaps not terribly well informed opinion and provoke discussion from those that have more knowledge of this course.
I think you are going about things the right way by asking lots of questions, but at the risk of sounding patronising and stating the bleeding obvious, don't just use OATS because it is the nearest school. Be sure to shop around, you may decide it is the best option for you... It was for me.
If you are really keen on buying a place to live in during the training, it might even be worth considering Eastern Oxford, Cowley Road type way where there are loads of university student houses and you should generally have no trouble finding tenants after you have finished. Just a couple of thoughts.
All the best.