Are you setting the ISO on the camera at 25? If the ISO is set at 25 can I just use the meter readings to set exposure?
Roughly, sure, but if you're metering visual light, the reading won't really reflect the amount of available IR light very accurately. It varies with time of day, for one thing---at morning and evening, there's more IR relative to the amount of visual light than at midday. (Stands to reason---same mechanism that makes sunsets and sunrises red.) Visible light scatters more than IR, so if you meter something that's lit indirectly, it will read brighter in the visible spectrum than in IR.
But like everything else in photography, it comes down to "think about it and understand how light works". It's just that in this case it's light you can't see.
I've always used the Efke IR film rather than Rollei---the Efke has more extended sensitivity, I believe---but I found it to be *much* easier than I was afraid of when I first picked it up. You have to guess at exposures a little more than you normally would, which means you should bracket and experiment to figure out what works in practice. If you ask me, that's half the fun.
Metering *through* the filter sometimes works, too. Different meters probably have different levels of sensitivity to IR, though, and again some experimentation is called for.
TLRs are great IR cameras, not just because you don't have to look through the taking lens, but because the leaf shutter is easier to handhold at slow shutter speeds as compared to an SLR. Leaf-shutter rangefinders should have the same benefit.
-NT