Does anyone believe she created her own email/server system just so she would have to carry only one device?

Maybe what you wrote there was carelessly phrased. You appear to be conflating two different issues.  What she said was,

Why did she use her own email account?

As the Secretary has said publicly, when she got to the Department, she wanted the simplicity of using one device. She opted to use her personal email account as a matter of convenience; it enabled her to reach people quickly and keep in regular touch with her family and friends more easily given her travel schedule. That is the only reason she used her own account. Her usage was widely known to the over 100 Department and U.S. government colleagues she emailed, as her address was visible on every email she sent. To address requirements to keep records of her work emails, it was her practice to email government officials on their ".gov" accounts. That way, they would be immediately captured and preserved in the Department's system

That doesn't seem so crazy to me.

There is another factor that some former colleagues say puts Mrs. Clinton's decision in a more reasonable light: the archaic, dysfunctional computer systems at the State Department. Only a tiny fraction of emails sent on the State.gov system in recent years have been permanently archived. And former State Department employees describe the unclassified email system in 2009 as frustratingly inadequate.

Using State Department email outside the building involved "incredibly unreliable software," said one former senior official. "If you had to write a priority message that was more than a paragraph long, it could leave you streaming sweat and screaming at the screen. And that's when people would turn to their private accounts out of desperation."

Another official described landing in foreign capitals late at night and having to go to the American Embassy and wake people up simply to check his unclassified email. He called the situation "ludicrous," though he said the system slowly improved, especially as more people got government BlackBerry devices.   LINK

And this:

The law, in fact, requires federal officials to use outside mail services. This isn't optional. It isn't the result of a desire of our leaders to hide their email. The law, in the form of the Hatch Act of 1939, officially "An Act to Prevent Pernicious Political Activities," specifically prevents the use of federal resources (originally, specifically postage) for political activities, and email is now considered one of those resources by the Justice Department.

Here's how that works. Let's say that while Secretary Clinton was in office, she wanted to talk to Bill about whether Chelsea would make a great president one day. That's a political activity. If that message were sent using government email services, it would violate the Hatch Act. Even if Mrs. Clinton sent that message to James B. Steinberg, who was her Deputy Secretary of State, it would violate the Hatch Act.  

She could send it to Mr. Steinberg via Gmail or AOL. That would be legal. But to send it (or any other political correspondence whatsover) via federal email systems is a crime.

That means federal officials almost always have one or more personal accounts. George W. Bush had GWB43.com, which was operated by SMARTech Corporation in Chattanooga, Tennessee. In fact, in my book, I estimated that 103.6 million email messages were sent by the Bush administration via the SMARTech infrastructure and were never recorded or preserved.

I consider that to be one of the greatest losses of historical documentation the U.S. has yet suffered.

Therefore, the fact that Mrs. Clinton had a mail server in Chappaqua is not surprising. In fact, given the Hatch Act, a substitute email solution would have been required.

 LINK

I am saying that the concept of putting a server in her Chappaqua residence was already in place for the Ex President of the United States.  GUARDED BY SECRET SERVICE.

And by the way, doesn't an Ex-President retain some level of security clearance?

Your own source from the Washington Post article confirms my point.

"Those briefed on the server setup say the device installed for Bill Clinton was deemed too small for the addition of a sitting Cabinet official. Instead, a server that had been purchased for use by Hillary Clinton's 2008 campaign was installed at the Chappaqua home."

"The role of Platte River Networks was to upgrade, secure and manage the e-mail server for both the Clintons and their staff beginning June 2013. Platte River Networks is not under investigation. We were never under investigation. And we will fully comply with the FBI," he said. [The Denver Post, 8/19/15]

Heh

As the GOP once again reaches out an inspiring, Lincolnesque hand to all frightened and frighteningly ignorant Americans..

The receiving agency, or a receiving U.S. contractor, licensee, grantee, or certificate holder acting in accordance with instructions received from the U.S. Government, shall provide a degree of protection to the foreign government information at least equivalent to that required by the government or international organization that provided the information.

When adequate to achieve equivalency, these standards may be less restrictive than the safeguarding standards that ordinarily apply to U.S. Confidential information.

Even Hillarys latest tormentor admits

Leonard, the former ISOO director, said this sort of information was improperly shared by officials through insecure channels more frequently than the public may realize,

Then

though more typically within the unsecured .gov email network than on private email accounts.

On the other hand these "improprieties" are so common they even have a name for them,

The difference in Clinton's case, Leonard said, is that so-called "spillages" of classified information within the .gov network are easier to track and contain.