1. Yes. Simply uninstall the 32 bit version and install the 64 bit version.
2. Yes and no. Some things should work e.g. Excel Integrated Reporting and sending/exporting a report to Excel. However places where direct interop happens, such as Send Contents to Excel from the file menu, and importing/exporting calendar data to/from Outlook might not not work
3. No. A 64 bit version the client should work perfectly fine with a 32 bit data service, and vice versa.
4. Latest 64 bit builds are available from here https://gb-kb.sage.com/portal/app/portlets/results/viewsolution.jsp?solutionid=200427112238351#

The general advice would be to install and run the 64 bit version of both Accounts, and Microsoft Office everywhere if possible. This is simplest and comes with no limitations around interoperability. However, in terms of Accounts itself you can freely mix and match 32 bit and 64 bit in any configuration. Really the only limitations come about when trying to integrate with Microsoft Office when it does not match the same 'bitness' as Accounts.

Hope that helps

1. Yes. Simply uninstall the 32 bit version and install the 64 bit version.
2. Yes and no. Some things should work e.g. Excel Integrated Reporting and sending/exporting a report to Excel. However places where direct interop happens, such as Send Contents to Excel from the file menu, and importing/exporting calendar data to/from Outlook might not not work
3. No. A 64 bit version the client should work perfectly fine with a 32 bit data service, and vice versa.
4. Latest 64 bit builds are available from here https://gb-kb.sage.com/portal/app/portlets/results/viewsolution.jsp?solutionid=200427112238351#

The general advice would be to install and run the 64 bit version of both Accounts, and Microsoft Office everywhere if possible. This is simplest and comes with no limitations around interoperability. However, in terms of Accounts itself you can freely mix and match 32 bit and 64 bit in any configuration. Really the only limitations come about when trying to integrate with Microsoft Office when it does not match the same 'bitness' as Accounts.

Hope that helps