Dear Rob,
Generally flowmeters, suction regulators and cylinder regulators are very hardy stuff and you can expect the equipment to last a significant long time if you maintain them properly.
If you have a significant quantity with each type of equipment, you may want to consider calling a tender based on economy of scale. Generally the price could be lower and equipment vendors inadvertently compete on pricing.
My experience with Ohmeda products is they are very reliable especially in the SOT range. Try standardise with 2 brands if they are good equipment so that you don't really rely on one vendor support when you need them.
Regards