The hosting feature pages say that 1 domain is free.
What are the charges for additional Unique IP Addresses if we take Shared hosting or VPS hosting?
The one free domain is the domain registration. The hosting plan (shared or VPS) lets you host "unlimited" domains. You don't need Unique IP addresses unless you have a special reason.
Yes we need unique IP for each domain. The reason has to do with SEO.
When you say unlimited domains, with they all share the same IP address be default?
Correct. One IP address is shared amongst many domains.
I've not seen any credible evidence that unique IP addresses help SEO.https://wpengine.com/blog/the-myth-of-the-dedicated-ip-address-for-seo/
The straight answer is $59.95 per annum for a unique IP. Plus $13.95 for a standard domain. Used to be the case you could use sign-up codes for various discounts including additional 'free' unique IPs. Not sure if those codes would still work to save you money.