First thing to confirm is that you want BBSHD over BBS 02, usually you would as the BBSHD has higher reliability than BBS02 as it is overbuilt, HD denotes heavy-duty.
Next you want to figure out what size you want. Confirm that you have a regular bottom bracket shell on the bike, if you just check out top of this thread it will go over how to confirm that, it's pretty easy. If you don't have a fatbike or a very old bike or some super high end mountain bike then you probably need the regular size BBSHD but it doesn't hurt to confirm.
We would also highly recommend clicking the questions and answers tab on the listing to check out our extensive documentation. Especially the top link which is to our wiki page. This goes over all aspects of installation and picking out chainring, doing modifications, tips and tricks etc, we recommend bookmarking this link for future reference.
Past this point we are just going to go step-by-step down the list of the available options on the listing.
You would use the 750 W option on the listing if you want that power level although it is easily configurable later for any power level you wish with the program cable.
For information on the chainrings as well as a video on picking out chainrings check out the top of this thread.
For the display you have a few options, there's no one right answer that's best here and there is a bunch of information about each one if you go to the individual listing for that display on the site. The DPC 18 is the only one with a USB port so if you want to charge your phone using USB port you might want to get that one. If you prefer a horizontal display go for the 750c version.
The gear sensor is not strictly necessary but it makes a great addition and makes shifting much more enjoyable. We have the documentation to the gear sensor on the individual gear sensor listing if you want to check it out.
For throttle choices we have a bunch of options, depending on whether you like a twist throttle like you might find on a motorbike, or the universal thumb throttle which is great for either side. We also have the left thumb throttle which if you are using on the left-hand side can make a great choice, but it depends on how you have the rest of the components on your handlebars arranged whether you can make use of this. If in doubt start with the universal thumb throttle you can always upgrade it later.
On the program cable listing you don't need this but it might be a nice option to have in case you ever want to change configuration options for fine tuning power levels and that sort of thing, also you can run the kit in a diagnostics mode using the program cable to bypass the display, which is a cheap and easy way to find out if your display is functioning if you are doing troubleshooting.
As far as battery options this is highly dependent on how much battery you can bit in your bike triangle and how much you can afford as well as how much range you are looking for. At a minimum you want to make sure that you make a cardboard mockup of the battery you are looking at and physically seeing if it will fit in your frame. You also have the option of selecting no battery and going with a battery that is not included in the list by simply going to the battery section on the site, not all of them are included in the options but the kit will work with any 48 V or 52 V battery.
Generally you want the biggest battery you can manage so you don't run into range anxiety and going long distance as well as having a long cycle life, larger batteries will get more cycles than smaller batteries if treated with optimal care. For more info on this and battery fitment please check out the documentation on the beginning of these threads:
For the charger we have essentially 3 different options. Standard, mini and advanced. Standard is dead simple, affordable and reliable. Mini is a good form factor, has important features like fuse and variable charge percentage. Advanced has the most features including a nice display, variable charge percentage and variable charge speed.