Thanks all. I found a 4x8 on "layoutvision.com" that I will probably go with.
Fall Mills RR. Does not look to difficult and it fits my current space requirement.
                                                                           Gene

Thanks to all,
    The info contained in these replies  has convinced me. Going to a combo of 22 and 18 and stick with the 2-6-0  steam and the four axel diesels until I can shake loose more space in the basement. For now 22 outside and 18 inside(two ovals) on a 4x8 platform.

                                                                                                 thanks Gene

Thanks to those who responded to my question on radius. My question was answered. I'll be sticking to Locomotives in the 0-6-0 to 2-6-2 range for now. Will try to free up some room so I can expand.

What is the largest Locomotive that Can be used on a 18 in radius?