No, transactions – regardless of status – won’t be affected by updating Trezor Suite. The coins and tokens go to the blockchains and are stored there, not in your Trezor device.
But personally, I’d wait to update Trezor Suite until the pending transaction is completed, because of status messages to Suite. If you don’t have to update Suite then you may want to wait until what you’re currently doing is done.
No, you can safely connect Metamask (MM) to your Trezor, but please wait with that until you’ve read about MM and know how it works and know what you’re doing. Most of the MM support in this forum are because people engage with MM before they know it properly. Always educate yourself before doing anything with your money.