The 8051 series is rather old and not all that well supported.
For a new design you would be better off using such as a PIC MCU.
You could use such as a 20 pin PIC18 series one for many different projects, or a 28 pin DSPIC33 series if you want vast amounts of memory.
The different versions have numerous built-in peripherals, such as high speed timers, serial / I2C / SPI ports, PWM and a range of others, so making an all-in-one device is relatively simple, hardware-wise.
There are rather more people on here that use PICs that use the 8051 series, so you are likely to get rather better support.
To program them, you need such as a PICKIT4 (or PICKIT3) programmer, which is readily available from many places.
The software is free, "MPLab X" from Arizona Microchip (micrrochip.com).
There are even ones as small as 8 pins (power and six input/output), but still a 32MHz CPU with many peripherals (pic16f18313).