I think whether to have one or two anchors ready at the bow is somewhat dependant on one's cruising ground, ground tackle, personal preferences, etc. But having two rollers sounds like a good idea to me, especially if you are already building your own platform. One consideration would be the fore and aft alignment of the two rollers. If they were in the same fore-aft position the widest part of the chosen anchors my conflict with one another; a slight fore-aft offset may serve well in this regard.
A related issue is how to secure the anchors and what to do with the chain/rode. I secure my Delta at the shank and at the crown, and would recommend something similar with most anchors that will remain at the bow. On my 323 the hatch/lid to the anchor well is built to accommodate one chain running to the anchor well. If I added a second anchor this lid/hatch would need to be modified.
Lastly, is the relationship of the bow platform structure to the bow chocks, and the resulting path that the rode will see when at anchor (I do not leave my rode on the bow roller when anchored). On my boat the rode lies gently against the platform structure, which serves to keep the rode from rubbing against the hull. If you have fittings or attachment fasteners be sure that they will not be a source of chafe to the rode.
Good luck!