Re: any buyer remorse?
Last I had from SL/XC is that they offer only hosted solutions but in some cases upon request they will supply the actual installation pack so you can host on your own. Whether this is still the case or not I don't know.
If these other big providers ask for $2000/month that's enough to put towards XC5 customization to make it your own. And after that simply maintain due to minor version changes.
You can modify templates directly with XC5 but I would advice against that. It is way better to do such modifications via custom module. That way you can make changes conditional, you can inherit from original template, etc.