@sandrabrown2
Here is a great article explaining everything about fusions:
https://connect.mayoclinic.org/discussion/spinal-fusion-2/
Its not clear to me what is being communicated to you. Already being fused L3-L5 is a loer back fusion. Possible he is talking about extending your existing fusion as this is common for the next joint to go bad due to the stress of the 1st fusion. If thats the case recovery should be pretty much the same as the 1st one.

As far as bending everyone is different going from 2 level fusion to 3 level I would guess you won't see a lot of difference in what you have now. My wife has 10 levels fused and can get most shoes and socks on (With difficulty) on but no tying. Now me I have no fusions but need one and can't tye mine as I have never been limber and the pain is limiting. I love my sketchers slip in.

Hope that helps
Craig