Ok. I found out why I was having problems. There are/were 2 issues....
First, designer errors using regular forms was caused by multiple problems (different DLL versions (GAC vs. local reference) and problems with AutoGenerateBindingRedirect). This was solved using the provided idea of absolutely killing all Telerik controls and installs, manually removing any remaining orphaned Telerik GAC entries(from older installs not using MSI which is what was causing a lot of issues), flushing all Telerik project references and license files, kill any binding overrides/redirects, then go back into solution and manually reference the DLLs not using the MSI to re-install.
Second problem is totally my fault for not paying attention.... I'm using VS2017 and attempting to use Telerik Reporting which doesn't have (as far as I can tell) VS2017 native support (goes up to VS2015), so when I tried to open an older report file it threw the form design error as well (but a slightly different one).
However, as usual, Telerik support is responsive and helpful. Many thanks. - John