This does NOT currently contain Cydia.
You'll have them when I decide you will.
Most likely. Said jailbreaks rely on a KPP bypass which inherently provides instability in the system, often leading to random crashes and kernel panics. Meridian is kppless, which means it won't suffer from this. That's not to say it will never crash - there may be issues, but on the whole, it should be a little more stable.
KPPless is a new style of jailbreaking which avoids writing to certain protected areas of the kernel. Substrate currently 'assumes' that it already has full access to those areas (which in this case, it doesn't), which causes issues when combined with kppless. Hence, Substrate requires an update before it will work properly.
Run the JB, and when it has worked successfully, open your SSH client and connect to your device on port 2222.
Run through the Jailbreak process, and click the 'Done' button. Then click 'extract dpkg'. Cydia should then be happy to open.
Please let me know if you are having issues after using g0blin/yalu/extra_recipe. If you're having issues with Cydia/jailbreak apps, use the Reinstall Cydia and try reinstalling said jailbreak apps.
Firstly, make sure your binary has been fakesigned with jtool. You'll need to sign with SHA1 for pre-10.3, but on 10.3 and newer SHA256 is fine too. Also check your entitlements. You can use these entitlements if you don't know what to use. If you monitor syslog you may see an 'i_can_has_debugger' message, in that case add the 'platform-binary' entitlement to your bin and you should be OK. It's worth noting that if you ran your binary before fakesigning it you may need to reboot and re-jailbreak first.