So I got my picocalc through the mail and some JESSPOW 18650 batteries from amazon and a pico 2 wh.
I have assembled it using the pico 2 wh and the batteries. When I try powering on, the power LED lights, but nothing on the screen 
Do I need to flash the pico 2wh before using it?
Does the included SD card come with a default image?
Yes, if you didn’t get your pico cpu with your picocalc order then you will have to flash the appropriate firmware into it.
It’s a fairly simple process and there are many examples and discussions on how to do here in these forums
This is what you want to flash if you just want to use mmbasic:
Yes, you need to flash the pico.
The sd card is just storage for your programs, data, whatever.
There is also this if you want to switch easily between your firmwares (UF2 files):
Don’t forget to update your keyboard firmware. There is a total overkill guide here:
But basically TLDR: all you need is a linux PC and stm32flash to do this:
sudo stm32flash -w PicoCalc_BIOS_v1.2.bin -v -S 0x08000000 /dev/ttyUSB0
so i programmed webmiteRP2350V6.00.03.uf2 and was able to connect via the USB terminal. That seemed to boot OK on the terminal.
Now ive put the back on again and left it connected to the pc via usbc (my batteries arnt charged). Still nothing on the screen when I power up. I think ive connected the screen ok, is webmiteRP2350V6.00.03.uf2 the right one designed to work with the screen? (I want to use the wifi on my board)
the light flashes on the pico 2 when i apply power
stm32 flash seems to stop at 71.12 percent
sorted this now and stm32 completes (I had downloaed the bin as ascii not bin).
but still blank screen
reflashed using the WebMite build built for the PicoCalc at Release PicoCalc PicoMite V6.00.03 · madcock/PicoMiteAllVersions · GitHub and that sorted it all.
Boots into basic now
Note that OP is using a pico 2 and I don’t support that yet (but check back in a couple of days )
Even if it takes weeks or months, I’m looking forward to your work. It will also put a fire under my butt and I’ll likely release an updated version of the PicoMite builds afterward. 
(I noticed Peter over at TheBackShed has been releasing updates for the official PicoMite lately, though the focus is only on the Pico2 now, and he only just recently started posting some source updates for those changes. So I’ll get a PicoCalc version of that stuff going at some point soon. Most of it seemed to be bug fixes and a few minor improvements, but he’s also worked on the display code, so it’s at least possible we might see a bit of a speed boost on the PicoCalc with that. I haven’t actually tested it yet, so I don’t know if it will have any effect at all, but I’m somewhat hopeful.
I’ve been enjoying learning and actually using PicoMite during my hiatus since the last build I posted. At some point I need to post the results of that too. Cut my teeth on a few smaller projects like a file manager and a pixel art editor (both of which could use some additional features, but are potentially useful as-is, since I’ve been using them myself lately. But I’m making steady progress now on a much more involved project that I think will be of interest… Let’s just say that porting Pico-8 code over to PicoMite BASIC is not as difficult as I imagined, but it’s still a lot of work and more time consuming than I would have expected. I’m not done with this project yet, but I’ve gotten far enough along to have some confidence that it’s going to be possible, as I’ve seen some of it working. (Just to be clear, this is NOT a Pico-8 runtime written in MMBasic. It’s a port of Pico-8 code for a specific game to MMBasic that I think will be a nice addition to the PicoCalc, and something I’ve wanted to play on the device for a while.)