Actuallly sandisk is the brand officially recommended by Lotoo, so don't worry about it.
But as far as I know, somehow a full size SD works more stable on a LPGT. So I recommend some full size sandisk SD cards that are frequently used in Single Lens Reflex Cameras which means they are reliable.
But if you have other devices that require small sized TF cards (micro SD card), it is OK to just use an adapter. I think sandisk works best on lotoo devices. My lexar cards are not as stable and reliable as sandisk.
For the plastic see through case, I feel you don't need them unless your are on a LPGT Ti. If you mean the screen cover they are included in the box.
The leather case comes with whichever LPGT version comes with high quality and durability, really satisfying no need to change.
If you really need a plastic see through case I know in mainland China I buy them from Lotoo on JD dot come or Taobao dot come official e-shop platforms opened by lotoo, but you may need to use chinese to buy them and shipment may be complicated.