I have crossed Biscay numerous times in both directions.
I would suggest going into Bayona or Corunna prior to crossing and getting up to date weather information. Biscay can be an absolute pig or beautiful. I always go straight across (but I am usually limited by time as it will be a delivery job) and go west of Ushant. You can come inside Ushant, possibly stopping in Brest, but make sure you check the tides if you go this way.
sea conditions can bear little relation to current wind as it may have developed deep in the Atlantic.
Keeping in deep water, west of the continental shelf is the best course IMO. If you do get caught in a strong SW gale make sure you have plenty of sea room to avoid getting caught on a lee shore.
As with all passages, good preparation is key and making sure you have sufficient capable crew on board - suggest 3 minimum.
From northern Spain to a UK Channel port should be 3-4 days.
Time of year - avoid autumnal gales if you can. To be truthful, I would do it almost any time if the weather was right
Hope that helps
Delivering boats for a living
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