[damien_ls]

I think this is a very good idea for many design agencies - it makes things so much simpler when you know exactly what your target platform will be.

Depending on budget, you may find a small managed VPS reaps rewards; you should be able to run your desired versions of PHP/MySQL etc. (and be able to control upgrades - or lack of - to suit software/scripts you develop), and also have the ability to apply your own branding.

Depending on what tools you already have in-house, it may also be useful for additional items such as source control server and/or project management tools etc. - and of course you could use to host your own website too...