some questions.

Well the more volts you run the more weight you will be carrying, but you get much better performance with more voltage ie more power and speed. The motor you are talking about I have no experience with so that I can't help you with that. A site for review I have never seen, but that does not mean there isn't one somewhere.

Yes you would get more range with a 40ah battery. The way that rating is supposed to work is you can get forty amps for one hour or 1 amp for forty hours as opposed to the twenty amp hour which would give you 20 amps for one hour ect. However you need to ask yourself at what point am I paying for amps I will not use.

If you never go more than 10 miles on your bike do you want to pay for a forty mile range battery. The BMS is very necessary, if you are going to use one 48v charger. The reason is that each battery will run down to a different level. The charger will run until the pack is at a certain level. In doing so without the BMS one or more of the cells will be over charged while bringing the lower charged ones up to full charge. Unless you plan to charge each battery in the pack individually I would definitely recommend the bms.

Good luck with the bike, it looks as though you are doing your homework and that is always a good thing.

Hi c.a.d. – Welcome. I can help with a few of your questions. BMS stands for Battery Management System. Any battery system is made up of multiple individual battery cells. They should all be at about the same charge (voltage) at the same time, especially when they are fully charged and also when nearly discharged. If they are not, individual cells can be damaged or ruined. A good BMS system will keep individual cells from overcharging. It also will cut the battery power if any cell is getting close to a low voltage limit. Reliability and quality are significant issues with any BMS. The one that comes on the batteries from EPS is reportedly not the best.

I assume you are considering the Thundersky batteries from EPS. They are a good safe choice but are quite heavy for Lithiums. 48V 40ah will add about 55lbs to your bike. They are rated 2C continuous, which means you can draw 80 amps from them (C times the ah rating). The 1500W Cyclone is rated to draw 31.25 amps at 48V but will probably draw over 40 under full power, so you might need the full 40 ah for that motor. Batteries that don’t have enough ah will “sag” under load causing the BMS or controller to cut off power and other problems. More ah also means more range.

It sounds like you will be going to college? Unless you are unable to pedal yourself, you might find one of the smaller Cyclone systems would be adequate and safer. You could go farther with smaller fewer batteries and you might be closer to being legal (750 W, 20 mph under motor power only) depending on what state you are in. Think about it - not many bikes will handle or stop well with 65-70 lbs of extra weight (batteries, motor, etc) at 35-40 mph. They just aren’t made for that. You probably don't need that much power unless you are going to school in Switzerland. Plus carrying 90+ lbs of bike into and out of the dorm won't be much fun.

I would suggest that you visit Endless-sphere.com • Index page. They have separate battery and e-bike sections. There are lots of reviews of vendors and discussions of products. There are several extensive Cyclone and Thundersky threads and lots of BMS info. You should find the answers you need (plus many more) by searching the forums there - jd

What type of battery you plan to buy? Lead based batts are OK without balancers , any other type (NiMH , Lithium) needs BMS - few reasons for that: For example Li based batteries are expensive , so you want to preserve them as much as possible; those batts can be sensitive (depending on a type) to hi current draw , so BMS protect it from that too...Goldenmotor has good motors (not my experience, but someone I know) , but you should really shop around more (google Chinese manufactureres, you may get more for your money. ie Crystalyte). Best choice at the moment, battery wise, are Headway LiFePO4 , if you can afford it ...
P.S. Just saw jdcburg's reply , so that is the best advise you can get.