If you bag a cluster of blossoms before they open you should be fine.

here is a site to check

http://www.southernexposure.com/index.html

http://www.southernexposure.com/open_pollination.p.html

http://www.southernexposure.com/lib.html

Here are some previous discussions that address your questions and should be of help.

Cross pollination question about tomatoes...

Blossom bagging?

Growing several varieties of open pollinated...

There are many more discussions too if you want to read them.

How far? With wind and insects? A llloooongg way but please note that many of us save seed without concerns for cross pollination because it is so minimal and with just a bit of care you can minimalize it even more.

I have grown mixed OP varieties for years and saved seed as well as traded with many others and have only encountered 4 maybe 5 CP plants. So is it worth getting the seed from plants that will be planted close together? Definitely!

Bag if you wish or select early fruit, plant interior fruit, and multiple fruit from more than 1 plant of the same variety.

Enjoy your tomatoes!!

Dave

Nothing is safe on a residential sized property if you have bees (tiny sweat bees and bumble bees) in the area. The bees are flying an appreciable distance from their nest chambers to the source of pollen so several dozen feet between plants is not a big deal to them, and at any one time relatively few flowers on a tomato plant have available pollen, as a result a sweat bee or bumble bee may visit most of the tomato plants in a general area befor leaving.

Distance mainly comes into play if you have large plots of the same variety distanced from plots of a different variety, that way bees can "fill up" on the pollen from one variety/plot [all the while cross pollinating those plants, but they are all the same variety so it doesn't matter].

In a garden of mixed varieties I can get a range of cross pollination of 0%-40% per fruit mid season when bee populations are high.

Bagging is not a problem (I get bags/wedding sachets at Walmart) if you only need seed from a couple of fruits (several hundred seeds). If you do not want to go to that little git of trouble, the first fruits of the season will often have a lower incidence of crossing because of lower bee activity.