Clarification regarding (deepTools) bamCoverage output
Yes
The total RPKM for the region in the bedgraph file is the value already present in the bedgraph file. If you want to estimate the RPKM for a larger region composed of multiple bins then you can average the per-bin RPKM values. Note that adjacent bins with the same value are merged by deepTools, so you will need to account for this.

Note that RPKM is NOT a robust normalization and that I should remove it from deepTools so people stop using it.