Pelidc is spot on. Listen to him. It is so easy to build cabinets that are not square, not strong enough, and poorly designed. I understand that you want to save money, but cabinets are not the way to do it. If you don't like the price of the big box stores I have three suggestions:
Look online for RTA (ready to assemble). A good alternative, and shipping is usually free if you purchase X amount.
If you have a recycle/reuse it store such as Habitat for Humanity, you may find that someone has donated perfectly good units that need a little TLC. You are capable of painting them and replacing the hardware, aren't you?
Some manufacturers have outlet stores, that dispose of overstock for deeply discounted prices. I don't know where you live, but there may be one within driving distance of your place. All you can do is look.
Another question you had was about the floor. Yes it is easier to tile and then install cabinets. Less work is involved. Trust me on this.
Continuous countertops have no functional advantage. It is easy to get an extremely tight seam between sections of virtually any material. After 10 seconds you will forget it is there. Focus your energies on something that matters, such as better kitchen lighting.....
If you want to save money on countertops, look at a couple of things. Wilsonart HD laminate is good stuff, and comes in a huge variety of colors, finishes, and textures. Easy to install and gentle to the pocketbook. Also, if you have a stone supply store, go visit them. A whole slab of granite is expensive. Remnants are not. They are just waste that they are happy to sell for a fraction of the normal price. One of my neighbors had a counter made out of three pieces, in a geometric design. It looks like a million bucks, but cost one third of normal. Or lay down some plywood, and use a product like this: http://www.daichcoatings.com/spreadstone_countertop_kit.html