It depends on how many ip addresses you have.
Q1> if you have 1 ip address, you should get the SAN certificate that handles multiple domains - http://www.ssl.com/subject_alternative_name gives a good explanation on what a SAN is useful for. If you have 1 ip per domain, then you can get by with a cheap standard SSL certificate for each ip address.
Q2> if you have 1 ip address, this would be where a wildcard comes in handy. If you have 1 ip per domain, then you can get by with a cheap standard SSL certificate for each ip address as mentioned above.