Oracle 12c (RDS) Questions from a SQL Server DBA
Index Maintenance: Generally speaking you don't need to rebuilt b-tree indexes because they are self-managed. 

When to rebuild Indexes?

Index Internals- Rebuilding The Truth

Integrity Check: Oracle has DBVERIFY(dbv) command-line utility for physical data structure integrity check. But you can't use this tool on Amazon RDS as it doesn't provide shell access to database server. 

 DBVERIFY: Offline Database Verification Utility

Statistics: The preferred method for gathering statistics in Oracle is to use the supplied automatic statistics gathering
job. Or you can gather it manually using DBMS_STATS package. Details are given in the following white paper.

Best Practices for Gathering Optimizer Statistics


  In SQL Server stats are automatically taken care of when a table grows by 500 rows + 20%, is there an Oracle equivalent?


How often we should gather statistics is depend upon how much changes are being made in the tables which affect the query plan. In other words when statistics become stale we need to gather statistics. You can set stale percentage threshold for a table using STALE_PERCENT(default is 10%) parameter of SET_TABLE_PREFS procedure under DBMS_STATS package.
For details:

DBMS_STATS

Tablespaces: You can define the increment size using AUTOEXTEND ON NEXT clause either in CREATE TABLESPACE or ALTER TABLESPACE statements.


  And also is it not better practice to presize these to avoid any growth during production hours?


Auto extending doesn't affect the performance noticeably as it doesn't happen frequently unless we specify very small size on NEXT clause.

CREATE TABLESPACE

 Important DBA and Performance Views: Some the of the important dynamic performance views are given below(v$ views).

V$SESSION: Currently active sessions.

V$SQL: SQL command recently executed and its related information.

V$SGA: Statistics related to Oracle's shared memory called SGA.

Dynamic Performance View Description

 Key Metrics


  On the above point, are the key metrics in Oracle the same as SQL Server, roughly? I.e. PLE, buffer hit cache, disk latency etc.


Generally speaking, these are same just Oracle has different terminologies to address them. For example, Page is equivalent to Data Block in Oracle and life expectancy of a block is determined by touch count algorithm similar to LRU(Least Frequently Used) algorithm.