I'm looking for advice from some real sellers on a couple things, because Amazon's FAQs are, well, big corporate FAQs that don't cover a lot of stuff.

Background: We're selling a bunch of items all FBM. A couple thousand SKUs, all our own brand where we created the listings from scratch. They're broken down into a couple dozen Parent SKUs, and then a ton of children per Parent right now. This is the "proper" way to list them as they're a "base item type," and then variations (color, pack quantity etc) of that design.

We want to start doing FBA for SOME of the variations where it will theoretically be more cost effective to have Amazon fulfill, but many we will only do FBM still. We plan to keep the FBM listings up as a backup even for the ones we start to do FBA. We were recently hit with the "Lost Buy Box even though our account health was fine" glitch, so I think doing FBA will mean we at least always have a buy box for those FBA items? We got our account fixed, but it was still very worrying, and lost us a lot of money.

Anyway Question 1: If we make a duplicate FBA Offer for our items, can I organize these FBA offers under a new "FBA Parent SKU" in the backend? I know the child SKU needs to be different, just append FBA or whatever, but can I make a parent SKU with FBA appended and have 2 separate "chunks" of listings?

The idea of having hundreds/thousands of unorganized free standing offers in my back end seems messy to me, so it'd be nice to have them grouped together the way the FBM listings are... But since the FBM SKU is the listing that CREATED the product, I'm not sure if just a duplicate FBA OFFER for that product can be organized like that, since that FBA offer isn't the one controlling the listing information itself? Or do duplicate FBA offers for already existing FBMs with a Parent SKU automatically organize under the original Parent SKU? I couldn't find anything about this, so am just wondering this detail.

Question 2: If I can organize it under an FBA Parent SKU structure, it seems like it might be easiest for me to just bulk create the FBA offers via spreadsheet for ALL my listings... Including ones I have no intention of actually doing via FBA anytime soon. Is this a horrible idea? Are FBA offers that you never send them product on going to cause any problems, effect metrics, or cost me anything etc? It just seems that it would be easier to do it all in bulk and then only send in what I actually want to do. Initially we may only send in 10-20% of our SKUs, but eventually it may be 40-50ish percent. It will probably never surpass that as our costs to fulfill are lower for the rest of the variants.

BONUS QUESTION: Seller Central claims 200-300% sales increased for some of my products by switching to FBA... Seems optimistic to me given that for many of the products we're already the top results in search, even unpaid. In the real world what kind of sales increases does anybody think I can really expect?

Thank you in advance for any help!