we do lot of turn-key projects upon the configuration u have asked for.

we use slaves based on 89c51 or 89c52.
there is a 8 pin dip switch on each controller board based on micro, which is used for setting the address therefore 256 unique addresses can be set.

use rs-485 which provides 32 units can be connected in one parallel chain.
all plug-in and out types.

provide optical isolation for all transmitters and recivers.

keep receivers in enable mode and transmitters in disable mode so as to avoid bus contention.

remember if 2 transmitters of slave become enable at same time it may lead to no data being received by master.

put an led on the tranmit/receive enable pins so that any faulty enable because of hardware problem may cause full communication bus to stop working for tranmissitions from slaves to masters. and led will help loacating the faulty slave unit fast.

use 18.432mhz xtal. this gives proper values to be loaded in timers registers.
higher value such as 24 mhz can also be put but then some errors 2% are unavoidable.

make software such that the slave respond - i.e make their tranmits ON/ enable only when asked to do so. depending on the unique address set thru switches.

if u further require some more help or want ready made design u can contact me.

bye