Continuing the discussion from Recommendations for Mk2 new wheels:
- My model of MX-5 is: __ MK2.5
- I’m based near: __
- I’m looking for technical help or recommendations on: __ New wheels for Mk 2.5 Nevada with 16" wheels, can anyone tell me what offset I could use in 16" mini lights or Mag lights to fill out the wheel arches a bit, just for the looks and be a little different
If you know the offset and width of your original 16s then you can use a calculator such as https://www.willtheyfit.com/ to make a judgement about what you want and where you want to be. Bear in mind you have to make a judgement about brake clearances with the wheel design you choose as the site doesn’t factor this in and ensure the centre bore (with or without a spigot ring) and stud patterns will be compatible. 
For instance, I was able to use the calculator to go an inch wider (7 up to 8") and an inch further out (et55 down to et42) with a larger tyre (205/45 up to 215/45) and managed to create 0.3mm more clearance inside whilst pushing the wheel face out by 25.7mm. 
That was on my nc by the way, but the principle is the same. Check all your clearances and you should find a setup that will work for you 