Need Help I want to chnage my site from CMS to Wordpress ?

Dear My Respected Seniors and mates

Need Help I want to change my site from CMS to WordPress having 20,000 page views and 10,000 Visitors daily.Site is 7 years old.I have some serious questions .

1. What problems may be suffer during or after shift Word press ?
2. May my site all loading and optimization issues may be resolved ?
3. Is it SEO friendly ?
4. Is it Optimization friendly ?
5. Is it beneficial for future ?
6. How i can save Hacking and Spam attack ?
7. Also please share your experience or any researched practical article on shifting site from CMC to word press.

It is the matter of my life as if i failed to recover site may be many employees lost their jobs.

Waitting for the thoughtful discussion .

Best Regards For All .

1) There will not be any problem. WP site will be built separately and then migrate to your main site to avoid downtime
2) WP has caching but if you install many plugins, you will still suffer some lagging. Your best bet is custom WP theme which only have optimized javascript files and images
3) Yes
4) Yes
5) Of course
6) We offer 100% spam and hack free hosting if you need. We provide daily malware scanner, PCI & firewall
7) What cms are you currently using?