Is there any way to know total number of features and sketches in the Feature Manager Design Tree other than counting one by one?
Performance Evaluation on the Evaluate tab will give the total number of features. I don't know of any way to count sketches, though there certainly may be one.
What is meant by rebuild time?
The time it takes for the software to rebuild a model from scratch. Basically hit Ctrl-Q and it's the time until you're then able to do anything else with it.
2018 SOLIDWORKS API Help - Traverse FeatureManager Design Tree Example (VBA)
Retrieving data ...