Welcome to the forums.
I'm not sure what an MFM would say about hospital bedrest starting at viability, given your case history. But I do know that we don't see that very often - mostly because the evidence supporting bedrest as any sort of therapy is pretty much nonexistent, and so they would only use it if there were good evidence that a) you needed constant fetal monitoring, or b) you were responding very positively to bedrest despite the lack of evidence for it in broad populations.
The tachycardia of 120+ sounds miserable.
Did they give you any medication to lower your heart rate? IIRC the way they are thinking about this right now is that sometimes the placenta turns up the maternal pulse.
Since you had it in two pregnancies, odds are you've got some sort of underlying condition that predisposes you to develop preeclampsia when you're pregnant. Have you had a workup to look for autoimmune conditions? Or do you maybe have chronic hypertension?
We've a lot of posters who've weighed their options after a second pregnancy; I imagine more of them will be posting.