I believe Julio has answered your question about IPServices vs. IPBase, but as to whether its better to stack 48 or 24 port switches is an "it depends" type of question.
You should find 24 port switches less expensive than 48 port switches, but the 48 port switches will likely be less expensive per port.
A switch should be able to provide a "fabric" between ports on the same switch rather than what the stack provides. I.e. performance might be better between ports on the same switch than between ports on different stacked switches.
More switches in the stack, for the same number of ports, reduces the impact of any one switch failing.
There's a logical limitation to the number of switches you may stack, so higher port density switches defer bumping into that limitation.
Basically, the above amounts to trade-offs that you need to consider.
For example, using one 48 port switch vs. two stacked 24 port switches, the former is likely less expensive and should offer slightly better performance but it offers no switch redundancy that the latter does. If you consider redundancy critical, the latter would be the better choice.
For another example, consider a stack of two 48 port switches vs. a stack of four 24 port switches. Again, the former should be less expensive. Which offers better performance depends on what ports need to exchange traffic. The latter only loses 25% of your ports with a stack member failure, while the former loses 50% of your ports. Which is better depends on how you weigh the two stacks attributes.
