Planning for High Volume transaction data in a SAAS Web app

First of all, this is a very open question, it's not really one that can be answered 'correctly' - but I will just not down some pointers.

With your filegroup based on geo information - I would advise that you split the filegroups based on the tenantID itself. You have that information readily available in all tables, and you could easily set up a partition scheme which split the data up based on their ID. This is also likely to give a more even spread of data than if doing it by geographical information. Here is an example of a partition function, partition scheme and partitioned table to get you going:

CREATE PARTITION FUNCTION [PF_PartitonSixes] (int)
AS RANGE RIGHT
FOR VALUES (
  1,
  2,
  3,
  4,
  5)
GO

CREATE PARTITION SCHEME [PS_SixesPartitionScheme]
AS PARTITION [PF_PartitonSixes]
TO ([PF_Fives_1],
    [PF_Fives_2],
    [PF_Fives_3],
    [PF_Fives_4],
    [PF_Fives_5],
    [PF_Fives_6])
GO

CREATE TABLE [dbo].[tblCardsPartitioned] (
  [ID] [int] IDENTITY (1, 1) NOT NULL PRIMARY KEY CLUSTERED,
  [CardNumber] [varchar] (16) NULL,
  [PartitionElement] AS [ID]%(6) PERSISTED,
) ON [PS_SixesPartitionScheme] (PartitionElement);
GO

The next thing I would say is choose your indexing strategy carefully. Pay particular attention to the tables that will be the biggest - how will they be accessed, how often etc. Placing your clustered indexes correctly can ensure that you have a database which scales gracefully. There is nothing nicer than sitting in the break room on go-live day having a coffee because you've nursed 0 problems for half of the day.

Another thing I would say is choose your transaction isolation level very carefully. SNAPSHOT isolation can provide great benefits for high throughput application, but you need to be sure that it applies to your situation.

Anyway, this isn't an exhaustive list by any means, because to be honest, your question could be answered in a whole book. But just some bits to get you started there.

Matt, thank you for your response, it really help me to start.