Is natural gas available? If it is you should spend the extra money to convert from oil to gas.

I would except I just excavated the oil tank a year ago and put 2 250g tanks in the ba$ement. :/

Bumpity bump bump bump

Went thru this exercise 6 yrs ago. Replaced a 45 yr old Crane boiler that had 2 circ pumps, 4 zones w/ Beckett burner.1 zone hot water other 3 zones w/ 1 thermostat and balancing valves.
This arrangement was replaced for efficiency purposes. I have several close friends that are either plumbers, oil burner techs or supply house clerks, all were in agreement (unusual) that a Weil-McLein Gold with a Beckett burner was the best route (Riello burner is an expensive option) along w/ 4 pumps and three thermostats. It is cleaned yearly by the friend who installed, he is amazed at how well it runs 12 months of the year.
Do not use any of the peripheral equipment from old boiler ie circ pumps, valves, controller. My oil dealer questioned why my consumption dropped precipitously. When I told him , he shook his head and grinned.Also beware that some these installers get residuals from the manufacturer or supply for using certain equipment.
Answer A . Do your homework, account for all equipment and start making calls, there is not much more work involved w/3 zones as compared to 5. Grainger is a good place to get ballpark figures for equipment.
Answer B/C.We have discussed,Weil-McLein Gold has since had several design improvements.
One other issue , you may want leave out the tankless hot water option on the boiler and add another zone with a hot water maker. And lastly make sure the boiler is sized properly
I do not work for Weil-McLein.

Great reply, thanks very much for taking the time. Your advice makes sense to me.

My current HW heater is a 5-6 year old Bock 32E with it's own burner. I wasn't planning on replacing that with a direct tank that heats from the new boiler because the Bock is still relatively new. That said, 1 guy who gave me a quote suggested I could sell it on Craig's, get maybe $500 though I'm not sure how realistic that is. The W-M I have now has served well for 27 years. Barring any known negative changes to the brand, my intstinct says to replace with W-M and I'll look into the Beckett burner. I think my current burners are Riello which have been anything but trouble free.

Again, thanks!

A better solution would be to keep the water heater and have another zone (1st zone) ready to go from your primary loop; this way when the water heater does eventually fail, you'll be able to install the storage tank and plumb the new tank in with ease.
You won't get $500 for that water heater on craigslist. There's just too many out there for sale for less $$ than that. $75-300 used is what they can typically be found for in much of the northeast.
The final question is, why is your boiler leaky, rusty and inefficient at only 27 years? That's a short lifespan for a forced hot water boiler and quite honestly the heat transfer efficiency hasn't changed all that much in the last 50 years for non-condensing oil boilers. If the flame-side surfaces are kept brushed down and the nozzle is sized properly and there hasn't been excessive leaking which has led the boiler to scale up inside it shouldn't allow you to gain much efficiency to replace it. If your burner efficiency is low it can be easily upgraded and a new combustion chamber (or cc reline) can be installed. That boiler should last 100 years without leaking.

I agree with berlin , keep the water heater. A hot water maker is pretty close in price compared to the Bock. I also agree that a forced hot water boiler should have a longer life span than yours. But they do fail. I know of two people that had failures with 5 year old Burnhams. One had had a push pin fail , the other literally fell apart, both were steam. They got new boilers and that's it, no burner, controls, safety switch or temp gage and no reinstall allowance.
My first house had a GE steam boiler that I converted to hot water in the 80's. It is still running fine, it was installed in 1955.
This house had a Crane,no problems, it was 45 years old when it was removed.Metallurgy today is an exact science (as compared to 60 yrs ago)the fudge factor back then was probably 50%, today 2% and cast iron is no longer used. Cast steel has been used for a number of years, this could explain explain failure

Thanks berlin, & jon, great advice, I've added an empty 6th zone to both quotes for no increased cost. Smart!

The failure may be due to our acidic water. When I bought the house in '95, there was no water treatment. We immediately added a softener (which everyone around here must have) and a pass-through neutralizer for the acid. Problem is it's a sediment bed neutralize and takes the water pressure down too much so I added a bypass myself and don't use it. Accordingly, the acide water could be responsible for the boilers failure at 27 years. Who knows. It's leaking on the inside, it's rusting on the outside and I've currently got 2 bad circ pumps that need replacing. Rather than put good $ after bad, I figured this is the time to start from scratch. Last quote for a Weil-Mclean/Beckett combo was $8100 (probably high but we live in the NY metro area, everything's high).

Thanks for the excellent feedback!

8100 is in the ballpark I install boilers in NNJ and that is fine gor the area. 27 years for a 68 w/m is the life expectency you wont get much more this is not a 1950's boiler. when a leak starts if not resolved right away it mushrooms and multiplies as far as rotting the boiler fresh water has 02 02 caused rot hence more holes. Pretty much you cant go wrong with either w/m or peerless for hot water.Riello is an excellent burner however is your install cant work on it dont get it as many mechanics seem to have a problem with these beckett is more reliable, and easier to work on for average mechanic. Also dont trash your bock yet that is an excellent unit do as they say and set up for an indirect in the future.

I replaced by boiler 4 years ago with a similar boiler. The Solaia SL4100 essentially the Biasi repackaged and sold by Boyertown furnace. I kept my 12 year old Bock water heater. I couldn't be happier with the boiler. Mine is equipped with a Beckett burner. I have three zone single circulator system. This boiler replaced a 45 year old Crane behemoth. It cut my oil consumption by 30%.