The preliminary space-planning and schematic design phase is the most important part of any kitchen remodel. A kitchen can be filled with beautiful materials and finishes, but if the layout and space don't work well, it's not a successful design. In kitchens, more than in any other room, a good space plan and flow are critical. Anyone who has tried working in a poorly designed kitchen knows this. 
When working on a project that's going to include moving things, opening up walls or doing an addition, I recommend that homeowners work with a kitchen designers or other professional to develop a schematic plan and get preliminary estimates on construction costs. This is a great way to keep your eye on the budget while you finalize the design. 
The alternative is to design the space down to the last detail and then get estimates on the materials and construction or send it out for bidding. The problem with the latter option is that most people become emotionally tied to the  original design at this point, and it can be frustrating to rework a design due to budget. 
Bigger isn't always better. I can't tell you how many times I've met with clients who told me they had abandoned a remodel years ago because they couldn't afford the design as it was planned. It took them years to get over their initial design plan and be willing to talk to another designer to investigate alternative options. Read on for some ways to avoid this.