If you wanna go 70mph, stick with the Zero. It'll probably cost as much as one (at least a used one) to build a bicycle that can be safely ridden at those speeds. (the first Zeros basically *were* high-end ebikes, more or less; maybe more dirt-bike like, rather like the Stealth series)
As for motors, you could use whatever motor would be capable of the power level needed to go the speeds you want in terrain/weather/road/etc conditions you have with the total weight (rider/bike/cargo/etc) you end up with. There's a lot of info about that sort of thing in threads about fast bikes around the forum, including a thread "I'm a noob and wanna go 50MPH" which has a LOT of links to such threads, at least the ones already around when it was made. There've been a lot of such threads in the years since then, too. Most of the time a motorcycle is a better answer than any form of ebike, for reasons that may vary depending on the poster. There are also a few threads about the Stealth bikes that will have info you could use.
As for range...if that battery is the size I think it is, it probably weighs 40-50lbs+, and is physically huge. There's nowhere to put it on most bicycle frames, so unless you have a big cargo bike with a large enough cargo area, or are willing to sling it on just one side like a pannier, the only other good option is to extend the toptube of a bike frame to stick out over a small diameter front wheel, and build a rack supported by that tube (kind of like CycleTruck), cuz you don't wnat it on a rear rack cuz it'll badly affect the handling, and you dont want it on the fork cuz it'll affect the steering.
I have a pack of EIG NMC cells that's 40Ah (14s2p) and it's almost 40lbs without a case around it, and is not small. IIRC, it's about equvalent to 1/4 (or 1/2, can't remember) of one of the old Zero packs that used them. If yours is a full Zero pack, or even just a half pack, that's still really big and heavy.
WIth that pack, on SB Cruiser, which with me on it is over 400lbs (probably 500 nowadays), I only get about 30 miles, and that's at 20MPH max, average of 14-16mph, but the trike is about as aero as a brick with a dragchute.
Regarding skipping the BMS....I wouldn't recommend it, unless you are prepared to manage the cells yourself, checking their balance, keeping an eye on a wattmeter on the bike so you stay within the middle 70-80% of the capacity of the pack, etc. If the cells are good enough, you probably won't ahve any issues as long as the pack isn't normally discharged down past the level part of the SoC curve.
The EIG cells I have stay in balance just fine, and I use no BMS, but I am rarely using more than 3/4 of it's capacity before I recharge it. Only once have I run it down to dead, and it stayed in balance after that, too, but I wouldnt' want to do that a lot. The primary reason I use no BMS is that I would rather kill the pack than have it cut out on me in a situation where I *must* accelerate or risk a collision, etc. That's a very rare thing, but it does happen, since I am riding in traffic near a shopping mall much of the time (all but a few dozen feet of my daily commute, for instance, is not in a bike lane; only the very last stretch right up to the parking lot has one, and that's brand new).
You mgiht be able to make that BMS operate without the rest of the electronics of the Zero, but you'd have to find out what commands to send it, and how. There may be info about that on some of the other sites that specialize more in the Zero bikes; could be some here on ES but I dont' remember them if there are.
Which BMS you could replace the original with would depend on what you need it to do, and which chemistry cell is in that pack (probably NMC but I don't know). Since that pack has a contactor in it, then you odn't need a BMS with FETS on the output to handle the full pack current, just one that can control the contactor to shut the pack off when necessary. There's probably BMSs in the for sale section here that would work.