1. Does anyone know how many member's one database can hold .
As far as I know, it can hold a countless number. As in, as many as you want. If you are referring too the NetEngine Accounts. Unlimited Number of Members.
2. How many database's can system hold? .
A MySQL Server, I have heard of people having as many as 300 Database's ( Indivisual Database's, Not Tables in a Single Database ) MySQL is very robust, so feed it and watch your resources and you should be fine.
3. When Searchawy is doing a search, must it be pointed to a certain database? or does it search all databases until it finds what it is searcing for? .
I think you mean "Search Tables.Fields"? Not Database's Searchawy only deals with it's own Database that you set up in the Configuration page of Admin. When doing a Search, it will search the "Table(s)" that the links/Descriptions/Keywords and so forth are located in.