- Descending below to maintain 1000ft vertical separation
Vs
- Performing small doglegs ( 30 / 45 / 60 degrees etc )
I'd go for vertical separation if possible (i.e., legal and safe). Dodging clouds laterally, although fun on the right day, just increases both your workload and the chances you'll inadvertently go IMC.
Also, any tips on ways of establishing how close cloud actuallly gets ( i.e whether it's within 1500m horizontally or 1000ft vertically )
There's no real accurate way of working out horizontal distance. The problem is that you can guestimate all you like but you never receive any feedback as to whether your guess is correct or not, with no feedback there is no way of knowing whether you should be changing your estimates. In the end you just fly far enough away from the clouds so that you feel comfortable. All I can suggest is to try and imagine an IFR aircraft suddenly appearing out of those clouds and figure whether you'd have time to take avoiding action or not.
To work out vertical distance you just need to spend time 1000' below a known cloud level and get used to what it looks like.