If you will be using bridge-based pressure and load cell transducers you should probably consider an SCXI-based system. This would require you to select a multifunction DAQ card (perhaps M Series), an SCXI chassis (SCXI-1000 or SCXI-1001) and some modules with which to excite your transducers and acquire their responses. For load cells and pressure transducers, the SCXI-1520 would be an excellent choice. Assuming your flowmeter will output a voltage proportional to flow rate, you should probably select an isolation amplifier SCXI module that would be well suited for general voltage input. The SCXI-1125 would be a good choice for these input channels.
Of course you would also need cabling and breakout accessories for each of these modules. I would encourage you to contact your local NI sales office so that you can discuss your application in more detail.