Welcome, Steve.
You need to buy two of the small Rohloff sets anyway to get two syringes with screw-thread tubes, one to use with clean oil, one to use with dirty oil. That should service your Rolloff-equipped bike twice at once a year. After that you can buy a bulk set of Rohloff oil, two canisters of 250ml, one of all-seasons oil, one of cleaning oil (also used in ultra-cold conditions as a winter running oil). That should last you about ten years.
Rohloff optimises available oils so that their official oil changes all the time, and is thus guaranteed to work with the Rohloff internals.
I was horrified to read that you contemplated putting oils with unknown chemicals into a Rohloff gearbox: you don't know the Mobil works with plastic gears and paper filters (by design, some of the oil will "mist out" past paper filters*), and if your gearbox ever has to go to the factory and they discover someone else's oil in it, they could easily refuse you service.
That Martin services Shimano gearboxes with the Mobil oil is not sufficient evidence for you to try it with a Rohloff. Basically, you should grasp that the Rohloff is a highly specific, almost orphan design because if it were designed like Sturmey-Archer or Shimano gearboxes, it would be too heavy for bicycle use. Sorry to sound like nanny, but sticking to Rohloff's service suggestions is the key to happiness with a hub gearbox that will be properly run in roundabout the time a Shimano gearbox lies itself down to die, and from there the Rohloff will go on, for practical purposes, indefinitely.
Yes, I know, if you read this forum passim, you will discover that I service my EXT click box only once in 5000km rather than every 500km as advised by Rohloff, but I've thought it through, and obtained a special quality of proven grease (Phil's) for the job, and if I'm wrong, it's an external part that can be replaced as easily as ordering another one from SJS and fitting it without tools because it is held on by a thumbscrew.
Enjoy your new bike.
* I'm a painter and so only too painfully aware that two papers which look and feel the same can technically be very different, and behave differently too when the paint is applied. For oil painting I have a couple of dozen oils that perform different, often mutually exclusive, functions but are all called "drying oils" -- that doesn't mean they are necessarily intermixable.