Guessing that rope will have less breaking strain than the chain, so if always need to use at least some rope then strength of the chain link not so much of an issue (as will have something weaker than the chain linking onto the rope anyway).
In regard to the windlass feeding - maybe have a chain counter and simply (manually) lift
the link over the windlass - even if you have to use some method of taking strain off the chain to do so (but an anchor
, plus 20 foot of chain not that heavy - even if likely hanging mid water).
Or maybe if 100' of chain and 200' of rope covers most of your anchoring
needs - add the extra (existing) 20' onto the inboard end, for occassional use.
Personally I would splash out for the extra 20 foot of chain.