Diltiazem should be tapered over a couple of weeks or longer under your doctors' supervision. I forget how large a dose you've been taking. Don't do what I did and stop it abruptly. Doing so will affect your heart's conduction system and is very dangerous. I have been on a maximum dose and found it impossible to stop this drug after a few attempts. I think these withdrawal effects are dose-related, so lower doses should be easier to discontinue. Be careful.
With Diltiazem, peak plasma levels are reached in 2-4 hours, while Norvasc takes a bit longer -6-12 hours. I have been looking into switching back to Norvasc because it has generally fewer side-effects. The incidence of edema is lower. When I was on Norvasc, I didn't have the edema problems. It seems though that I am stuck with Felodipine for now.
Zebeta (Bisoprolol) 1.25mg is a baby dose. You should be OK with few or no side effects. I am on this drug also. This beta1 blocker does not seem to bother me as much as the beta2 I took previously did.
Instead of starting Norvasc at 5mg, why not start it at 2.5mg? Remember, you want to keep the side effects to a minimum and the 2.5mg dose might be enough. With Norvasc, you have to wait at least 7-8 days of consecutive dosing to see if it works. (Don't skip days!!!) You can expect a reduction of 13/7 or so in your pressure if your hypertension is moderate (sorry, I don't remember).
There could be minor interactions between the drugs mentioned. You are taking fairly low doses of these meds, so I doubt you'll have any problems. Things to watch for: your serum potassium and blood glucose should be monitored when Hctz is combined with Bisoprolol.
Norvasc and Bisoprolol - there may be additive reductions in heart rate, cardiac conduction and contractility - contact your doctor if any problems or heartbeat too slow.
Hctz with Norvasc - antihyperensive effect could be additive.
I don't think you'll have any problems because of the low doses. Always contact your doctor if not sure and report adverse reactions and/or side effects.
Good luck! :)