The first being a "mini" model. Everything remains the same, except for a smaller form factor. To reduce the price it will have a smaller screen, and a smaller battery. Possibly no storage options but comes bundled with a 32gb SD card. Also cheaper materials while maintaining the integrity of the console. Aim for a price point of $200. Keep the standard version available for $300.

Not really possible with the current Switch's design. A mini version would have an SoC of the same size (which would put out just as much heat), but would have smaller cooling strips and fans. Meaning it would have a diminished ability to maintain its internal temperature (which would lead to overheating issues), unless more efficient cooling methods are implemented. Other Nintendo handhelds that had miniature versions didn't have this issue, because the smaller size was still sufficient to keep them cool.

The second (and I believe more likely) is a "pro" model. Same form factor, but updated internals. If memory serves me correctly, the current model uses a customized tegra x1 chips, this model would use the a customized x2 for better resolution and frame rate. And would be treated like the PS4 pro or Xbox one X were games are required to be playable on both. This would retail for $350 and the base model would drop to $250.

Not possible. The nVidia Maxwell line of SoC architecture ended with the Tegra X1, which the Switch's chipset uses as a basis. With nVidia having since moved on to Pascal (which the X2 uses) and Volta. As such an more powerful SoC would use a different architecture than the existing Switch's SoC. Meaning a more powerful Switch model wouldn't be able to directly run the regular Switch's games without emulation.