1) You'll lose access to the PS1 exploit, but TheFlow is currently working on adding PS1 support to Adrenaline (which is the 3.60 eCFW). You can use a native Vita PS1 emulator from Retroarch which offers better resolution (instead of upscaling from PSP mode), but some games can run a bit laggy. PSP games are playable now, and Adrenaline offers a few different graphical filters which make PSP mode a bit more easy on the eyes.
2) Since you have an exploit game on 3.18 already (and I assume that means you're activated) you can just use the Adrenaline Easy Installer to install the new eCFW over your initial 3.18 exploit game. It's an easy 3 step process basically. Follow the very top instructions here:
http://gbatemp.net/threads/installing-adrenaline-6-61.449344/
3) Remote play doesn't work AFAIK, maybe if your Vita was already setup with your PS4 beforehand but since PSN spoofing is broken now you'll likely not be able to.