The previous posts address the "how to tell the client" concern.
However, you mentioned several quite separate but interrelated new costs:
* One: going ltd - in my opinion very wise. I recommend doing so as soon as finances allow for the added "respectability" as well as the easing of liability insurance and tax rates. Discuss with your accountant, there may be several options to consider.
* Two: taking on an office - if you just need additional space moving to larger accommodation might be more cost effective. If meeting clients in "your own office" is necessary there are many options, investigate them all. Remember to factor this and related costs into your new rate(s). Can you justify such an increase all at once or should you institute several smaller increases over the next year or so?
* Three: taking on employees - the biggest bloody step in business. Remember that an employee will cost you at least 50% more than the wage you pay him/her. To be safe budget 200%. Can you grow the business enough to cover this additional expense? How soon? Do you have the funds to cover costs until additional income meets the additional expense? Do you understand the paperwork required? Have you budgeted that time you will spend away from production? The reason so many of us "small guys" use sub-contractors is to sidestep these issues. Take the time for careful analysis and discussions with your solicitor and accountant.
* Four: buying your own house - if within your means by all means :-)
* Five: rates static for several years - inflation has been low but still eating away at value so topping up is certainly indicated.
If you have a running Business Plan "war game" the various numbers. If you don't I suggest you take the time to create one. The changes you are contemplating equate to starting anew. Don't guess.
Once you are clear on all the costs (business and personal) plus a profit margin you can determine hourly/daily/project rate(s). But not until then. Before that is just guessing.
Then comes the marketing:
le_gber ltd is pleased to announce the grand opening of their new premises at <insert address> ...
le_gber ltd is pleased to announce the addition of <insert name> to their highly qualified staff ...
le_gber ltd is pleased to announce a new pricing format adjusted to meet the changing requirements of todays client ...
A simple price increase is not what you face. A major sea change by several orders of magnitude is.