Hi,
First of all you have to devide your total project into segements.

like, RTC, Timer, Keyboard for time setup etc, Output to display.....

Next you built all above one by one as seperate routine and try them out as seperate project.

At last you append them one by one and test after every amalgamation of codes.

You should use simulator in order to check your codes. It minimizez error level and you will save time.

You can build all segments with one single micro. for out put display, you may need to use ULN2003 as output driver for multiplexed 7seg. and use 4 IO lines to select the digit to be displayed. You can multiplex them at around 120Hz.

When we multiplex the display usually they look little bit dim. you can use a 6 to 9 volt power with 470ohm resitor in series in order to increase the brightness of LED display.

with 6MHz crystal, you can built an acceptable accurate SW RTC. you can assign 5 int. RAM location, as
Tick,
Sec
Single minute
10s minutes
Single hour
10s hour.

Use any of 8052 timer with calculated value, and at every Timer overflow interrupt, a tick will be decreased, if tick becomes 0 it will be reloaded again with set value and increase second, if seconds reached upto 60decimal so it will be reloaded by 0 and increase single minute. when single minute reached upto 10decimal, it will reset by 0 and 10s of minute will be increased.

With this arrangement you are already getting single digit BCD value, so no overheads for converting from hex to BCD. You can use a lookup table where you can store a predefined 7segment data according to BCD digit.

At every minute increment, you can define a routine to perform many things, like display update, every minute, Timer check will be performed every minute, and anything you want to perform on basis of real time.

By using above technic you will need just 11 io lines.

You can have a full 4x4 matrix keyboard by sparing 8 io lines.

still you will have enough io lines for performing many jobs.

If I was at your place, I will use a 89C52 with 8k flash, and a watchdog timer. thats it, and I think you can built watch dog timer with a simple 555.

One 89C52, one ULN2003 and one 555 with 4 digit driver transistors (i prefer mosfets) and very few passive components you can built your project.

Believe me, it is not difficult, but will take you few days, if you build them one by one.

Goodluck

Rauf