How to link ALU to registers, RAM and Clock?
Just about every CPU will have an accumulator register to store one operand (and the result) of a math operation. You'll also need at least one other general purpose register for the other operand. From there, it depends on how much functionality you want to build in: you'll probably want another general purpose register for temporary storage, and if you want to access memory, you should have register(s) to store the addresses. You might look into the 6502 processor for an example of a simple register design (that is nonetheless very efficient), and the Z80 for an example of a much more complex design.

To interface with RAM, you'll need an address bus and a data bus. These account for most of the pins on a typical CPU: for example, to address 64k of memory holding 1 byte each, you need 16 address pins and 8 data pins (unless you work for Intel, in which case you probably kludge it to use 12 pins total, and drive the people who use your chip to drink :) You'll also need some way to enable the RAM (i.e. chip select) and set it to read or write; look at the data sheets for typical RAM chips and get to know the pinouts.

For the clock, you'll need an input for the signal itself; you might want to have an output, too, since the purpose of the clock is to sychronize all the chips. You'll have to change your design to implement the fetch/decode/execute cycle in time with the clock signal: that's beyond my understanding, but any good book on digital design should tell you how.

Good luck!