Track is the basis of a railway. It has to be laid right but also the layout and structure has to allow a flow in operation. Turnouts, or 'points' may need to be positioned with a little 'modellers licence' and not always exactly as the prototype as we have to consider the locomotives, rolling stock, and the fact that we are using electricity through the rails to make it work.
Stick to your plan ...
Golden Rule 3 - Be meticulous!.
Once the boards are built and supported test fit the track, and most importantly, take your time. Cut the track neatly and file burrs off the cut ends, make sure fish plates (joiners) are a good fit. If using live frog points, work out where any isolation cuts are required. Decide how you are going to ballast the track and what method of point operation you are going to use as this affects where various holes are needed in the baseboards, and how you disguise them later. Most importantly - stick to your plan and don't 'bodge' anything!!
When happy with the fit, pin it carefully having drilled any holes needed for point motors or mechanical rodding and be meticulous in your work.
It may be better to fit any point motors next although this can be left until after ballasting is completed. If you have drilled all the required slots/holes for the point actuator pins with enough clearance, then ballasting next is fine. If you need to lift any points to tweak any holes then leave ballasting until afterwards.
There are several methods you can use for ballast. Foam underlay is the quick and easy method but not cheap, although it does quieten any running noise considerably. Dry chipping laboriously laid then wetted with diluted PVA glue is the most often used method. It is painstakingly slow and requires patience and care especially around points. It's easy to glue a point blade and ruin it. Running noise can also be made worse with this method but it does look the most realistic when done properly.