Harold and Ann,
Your questions concerning your weight are quite common. As Lori suggested take a look around at some of the swinger sites, you will find that swingers cover every spectrum of weight and size. The key is that you are happy with the size that you are. A low self-esteem will scare many more people away than extra pounds ever will.
There will be some people who will judge you solely on your weight alone and for that reason won't want to be with you. There are many others, tho, for whom weight will not be a factor.
Regarding your penis size, this has been a hot topic of late in a few other threads. Again, some will not want to play with you because of it, others won't care. I would say tho that since you are aware that it may be an issue, make sure you are boned up in other areas (oral sex). It takes more than a penis to please a woman.
Here are a few links to other topics that might be of interest to you both in regards to your weight question and the question of penis size.
When Your Wife is Average Size and You are NOT The Body Beautiful Height/Weight Proportional - yeah right! Does Weight Really Matter? Accepting of BBW?
As you can see some of these topics have gotten quite heated... but they should give you a good idea as to the variance of opinions and what to expect.
And on the Quesiton of Penis Size:
Penis Question Penis Size, Is it Really Important?