How many MX records I can have?
You can add as many MX records (http://help.hostinger.com/185941-How-can-I-edit-MX-records) as you wish, however, it's highly recommended to keep an eye out for the priority values you set. Lower values denote higher priority, with 0 being the highest possible priority. If you assign multiple mail servers the same priority, then when that level of mail server is needed, mail will be distributed to those servers randomly and can cause issues.
How can I manage my DNS records?
With our DNS Zone Editor you can easily and fully edit your DNS zone, add and remove various DNS zone record types. You can access it from your hosting account's Control Panel
You can manage A, CNAME, MX, TXT, AAAA, NS and SRV records. All of these records will have their own section, so you can have everything managed and easily accessible.