That's a nice set of hardware planned! Were you thinking about getting the video slot addon card for the MNT? That will let you pass through the MNT the native Amiga screen modes. It's not a flicker fixer but at least you would be able to just use one monitor for RTG and native. The MNT is a very nice card and is only getting better as the developer releases new firmwares for it. The last one was a fantastic upgrade. The only thing that is a bit of a pain is that you have to take it out of the Amiga to update it. So if you have the video slot adapter, the MNT is going to be on the bottom slot under everything else which can be a pain. May want to consider putting the X-Surf in the next slot since it is so short to make it easier to remove the MNT or the BigRam which is easy to remove and get out of the way since it's not screwed in.
One thing to be aware of is a problem that some RapidRoads have with hot plugging. Several people have had their RapidRoads die after hot plugging thumb drives - removing one and inserting another while the machine is on. Most of them have been attached to the clockport but some have also been on an X-Surf. Apparently there's no way to tell if you have an affected one or not except by trial by fire unfortunately. When it was first reported Jens replaced some under warranty but now he's blaming the user. Doesn't necessarily mean that your card will be one of the "lucky" ones though.
One solution seems to have a powered USB hub plugged into the RapidRoad or X-Surf USB ports and do your hot swapping on the hub. It's certainly not an elegant solution but it works. As much as this stuff costs, I tend to take the perhaps overly cautious route
Were you thinking of getting an accelerator some time? If so, you may want to consider saving the cost of the BigRam and put it towards an accelerator that has memory on it, maybe with SCSI on it for the fastest drive transfers? Memory on an accelerator will always be the fastest memory because it is not going through the Zorro III bus or to the motherboard memory which is also slower.
The BigRam DOES work and works well. The memory speed may not be an issue for you. For most things I really don't see it being that big of an issue, just something that is. If you are thinking of installing OS4 the BigRam is not officially supported. It works for some, doesn't work for others. Sometimes putting it in a different slot helps. If you're going to install OS4 you will already have an accelerator with local memory slots available so that would eliminate the issue
Of course buying an A4000 accelerator can be a bit pricey these days. That's an understatement