I have just moved from ho and oo to n and have a mehano speed controller from a cheap set I got. Would this work if I soldered it to the track? Also I am going to have a two track loop connected with points and crossings but with 2 different controllers would this work?

The Mehano should get you going but it may not be as well "tuned" for N gauge motors.  Be wary of the maximum output voltage it gives out.

Running two loops with two controllers normally means you need to make sure the crossover points have isolating joiners. You cross from one track to the other simply by setting both controllers to the same direction and speed.

A more advanced way of running such a layout on DC is to split the track into sections, each of which can be switched to either controller - this is often known as "cab control".  You switch whichever sections you want to run your train all to the same controller and just drive along. So for example this could be the sections on either side of the crossover.     I've used cab-control style wiring on my layouts since the 70s.

Note that if you have a twin track controller the windings in the controller for each track must be separate as per Gaugemaster or Morley controllers
(other controllers are available)

Thanks probably will use insulation if I can get another controller. Can't seemed to find them in Britain except on EBay.😀