Blossom Bags: When and How Long?

[mms]

I came here tonight to ask this question and saw that there was already a thread about bagging, but it didn't contain the info I need.

When do I want to put the bags on?

As soon as I see the blossoms starting to form maybe?

And, how long do I have to leave them on?

I have read about bagging on several websites and a chief concern seems to be blossom drop. Any suggestions on how to keep them from falling off?

Would a larger bag give better air circulation, and as a result keep the temp down, possibly preventing blossom drop?

I saved seed last year but had enough distance between plants to be relatively safe. This year I am growing many more Tomato varieties and will have to bag if I am going to save seed.

Any opinions on barrier crops?
Do they really make a difference?

I have read articles where it is said that other blooming vegetables will draw insects away from Tomatoes.
I have also read articles that said to increase pollination you should plant other crops that insects like so you can attract more. Both opinions make sense, but the results are different.

Any opinions and advice will be greatly appreciated.

Thanks,
MMS