1. If HTTPS inspection is enabled then what is the impact on CPU+Memory utilization?
For powerful firewalls, you wont see much impact at all.
2. Is it possible to install various types of certificates like wildcard, SSL, and so on for various services?
Yes, they are, see point 23
https://support.checkpoint.com/results/sk/sk65123
3. If I enable the HTTPS inspection blade, does it automatically inspect both inbound and outbound traffic? If yes, then is there any option to separate?
No it does NOT, they are totally separate and inbound inspection needs its own cert (.p12 format) imported.
Andy