The anchor locker on the 40 Ocean fits 75m of 8mm chain easily. There's room for more, but as the galvanizing wears you do have to knock the pile over on retrieval, else it stacks up and jams under the windlass. I'm however not sure if the 38 Ocean has the same size anchor locker - the shelf looks different at least.
In most situations 50m would've sufficed us (depends on sailing area of course), but we were glad to have the 75m on occasion, more so lately as we discovered the benefits of anchoring further out in deeper water (less busy than up front and no charter boats, except the ones drifting past). Extending with rope would've been possible in every case, but it's definitely a convenience to just reel in the chain. Splicing chain to rope I can't recommend either, makes the chain rust like crazy.
I hope there's a cover for those electrical terminals on your new windlass motor!