I must've missed something, but why do you want the ROM switcher? Is it for some backward compatibility with your bridgeboard that you need 1.2/1.3? IMHO, if you're booting your Amiga off a hard drive and have tons of extra RAM available, why not just WHDLoad games to solve compatibility issues with older versions of the OS? Stick 3.1 on there and be done with it.
You are going to run into challenges with your Rev. 4 board. Right off the bat I can think of two: you'll need to relocate or replace that capacitor to physically fit the Indivision (as Pat mentioned), and the limitations in your chip RAM. Of the 1MB installed on your motherboard, Rev. 4 generally defaults to using that as 512K chip and 512K fast. Since you'll have the 8MB of fast on the GVP card you really want as much chip as you can get, from other places. In your case you're going to want to convert that extra 512K on the motherboard into chip. This usually involves replacing your Agnus chip on the motherboard with a newer model (8370 or 8371 --> 8372) and changing a jumper or two. Minor soldering may also be required, it's been years since I've done it, I forget exactly but instructions should be easy enough to find.
https://en.wikipedia.org/wiki/MOS_Technology_AgnusThe last consideration with your Rev. 4 motherboard and OCS Agnus are if the Indivision will work with them. It was mentioned earlier that it needs an ECS Agnus. This may not be the case (I can't think of why it would need that), so you'll be a guinea pig on that claim.
You won't require the ECS Denise unless you want the full ECS chipset. Not required with the Indivision, but some of us just like to have it. Again, just IMHO, I would buy it for that price. Just to have it.