With DCC, the criteria for separate power blocks is as follows:
1. Will you use more amps than you currently have on existing track block.
2. Do you need to isolate shorts, to prevent one bad Lok from shutting down the entire block.
Note that if you have at least one block (Segment, district).
Amps, plan on 1/2 amp per Lok. Actual usage varies per Lok, motor efficiency, length of train, up or down inclines, etc. Generally, 4-5 loks can run on each block.
Shorts are common with bad track, bad Loks (Especially steam!), operator errors. If you are having these issues, the more blocks the better.
One common pattern is to have the DCC system fees only boosters, not directly to the track. Makes the DCC system more stable, and last longer.
Note that with DCC, more than one operator can operate trains in any block. You just need the throttles.