Hi, i Use a mocal setup in my conversions with a 16row mocal oil cooler and a mocal thermostatically controled sandwich plate, but like you said if your running a oil temp gauge there are 2 ways of doing it, 1. using a sandwhich plate with cooler takeoffs and and a inline thermostat on the pipework. or taking the temp from the oil pressure sender ect... or 3 drill and tap the thermostatic plate and plum your sensor into that.
The standard thermostatic setup normally costs me around £180
and if your running an inline thermostat will cost around £220 thats including pipes, connectors, clips. all you should need to buy is a new oil filter (recommended)
You could fit a larger cooler, but it all depends on if you have space to. you could either locate it behind the passenger side bumper vent (where the indicator is) or in the middle behind your fmic if you have one if your have a large bumper and if it wont fit anywhere else.