As someone who spent over 25 years 'modelling' tramways at 12ins to the foot scale and was co-editor of the UITP/International Public Transport ''How to design and deliver a tramway'' notebooks maybe I can help;
It is claimed that the minimum curve radius for a modern tramway is 25m, that is enshrined in the BOStrassenbahn regulations,,,but that is Germany...elsewhere it is recognised that 17-18m is acceptable for modern articulated cars, with cities like Prague having curves down to 15m. We are talking standard gauge here, metre gauge trams can manage tighter curves - down to 11m on some Swiss systems and in Lisbon.
A very rough rule of thumb is Minimum Radius = track gauge x 11.
In the pre WW1 days minimum curves tended to be 45ft for standard gauge and 35ft for narrow gauge. In the USA they would get some pretty massive interurban cars round 45ft 'corners'!
Scissors x overs are used, we have one in the UK at Wolverhampton, I have seen a nmber in E Europe and there is at least one in N America.
The general 'rule' for track layouts is 'If you can imagine it someone. somewhere has built it'
Hope this helps