So I guess I will have Image + stereo sound.
Yes.
Will it work on BV7-32 with beolab 7.4 cause this is central speaker. and later on will I be able to play sound on bl7.4 + Pentas or Bl6000?
Yes and yes.
In the BV7 menu Speaker settings you will select ‘Speaker 1’ and the sound will be output from just the centre BL7.4. When you add additional speakers you will have to change the speaker setting menu to include the Pentas or BL6000s.
I think that not all BV7-32s are HD ready, but if you use the Audio Extractor that I listed first in the other thread it should strip the HDCP and the picture will work OK. If you get a BV7-32 that is HD ready then you may be able to use an Audio Extractor that also has a digital coax output, allowing the TV to process surround sound from the hdmi source. I have not tried this!
For info, this old thread describes using a BV7-32 with hdmi source: https://archivedforum.beoworld.org/forums/t/41059.aspx