Decimal display is tricky. A decimal display will involve repeatedly dividing your number by 10 and extracting the remainder. Division by anything that isn't a power of two is non-trivial, and usually isn't implemented in designs for simple computers (and therefore probably isn't reasonably achievable with the one you're currently working on). You could do it as a program, but the program would be pretty large, and again the kind of computer you're talking about often doesn't have much space for interesting programs (what size memory do you have? 256 bytes? if so, division would probably use up most of that).
Much more achievable is either hexadecimal (base 16) or octal (base 8) display. These only require division by powers of 2, which (like division of decimal numbers by powers of 10) is much easier to implement: you can just take a bunch of bits and decode them: for hexadecimal take chunks of 4 bits starting from the least significant bit of your number, while for octal you'd take chunks of 3 bits.
You could then use an off-the-shelf chip to decode those bits to the correct signals to get the digit to show on a 7 segment display. For octal output, the 74LS47 (or 74LS247) is a reasonable choice, but it doesn't handle hexadecimal output. For hexadecimal, an ICM7212 is one way forwards, although it's a bit harder to interface as it's designed to drive a multi-digit display but only has a single digit input at a time. They're also not exactly cheap. You could also build a decoder from an EPROM, which may be easier and cheaper, if you know how to do that.
