a. Custom, Case Management and Form records are all saved in exactly the same table in the database. This mixture of different types of records is handled by giving each type of Custom, Case Management or Form record a unique record-type number. So if Sumac searches to find all the Custom 1 records, it searches for all records that match the user's search criteria and also have a record type that means Custom 1.
b. Because Custom, Case Management or Form records are in the same table, they have exactly the same set of columns. One minor variation from that flat statement is that Forms must always be connected to a contact, and there are a few other things that Sumac tracks about them automatically that it does not do with Custom and Case Management records, so there are a few count, date, and text fields (two or three of each) that are pre-assigned meanings in Forms and hence not available to be defined by the administrator who is setting up a Form definition.
c. A field used in one type of record does not restrict its usage in another type of record. For example, if Custom 1 records use Amount 12, then that same Amount 12 field can be used for some different purpose in other types of Custom 2 or Form records.
d. The one area where point c. may be seen as an issue is with the Lookup Lists for Custom, Case Management or Form records. There is only one of each of the Lookup Lists used in Custom, Case Management or Form records. If Custom 1 records use Lookup List 12 to hold a list of fish, then it holds a list of fish in all Custom, Case Management or Form records. Lookup List 12 is one list in one place in the database. Custom 2 cannot use Lookup List 12 to hold a list of Shakespeare plays if it already holds a list of fish.