calculating and maintaining Database performance

ANyone please provide me solution for this if possible.

Current DB size = 300GB

describe process to take  to evaluate the requirements needed for to maintain database performance,

Some details need to be taken into account:

1. Growth of data is  between 50% and 60%.
2. Queries table currently partitioned manually (using views) by month with current monthly tables over 3GB. 3 years of data over 26 monthly tables.
3. Additional table in place with data growth of over 10 million rows a month (no partitioning)
4. SQL Version = SQL Server 2008 Standard.

If you have sample/ template of any documentation would be nice:

-         SQL Server Proposal document

-         Architecture diagram

-         Hardware/ software upgrade doc and diagram

Thank You , Shan Ali Khan