Emulsifying (and stabilizing?) a sesame oil ice cream

It seems that what you are trying to produce is a thin mayonnaise. So:

Will it be possible to create the emulsion with just a spatula and a pot?

No. You will have to really emulsify the stuff, preferably with something with a motor. Look into ways to make mayonnaise.

However, that would probably be wasteful, especially because the acetic acid would rapidly volatilize at 50°C. Do I have any other options besides citric acid?

In practice, standard mayonnaise, hollandaise and other yolk emulsified sauces do perfectly well with vinegar. Also, you are making a logical error here - if pure acetic acid boils at 50°C (something I've never bothered to check) this doesn't mean that you will get the acetic acid boiling out of a complex mixture of vinegar, oil, yolk and other stuff taken to 50°C. You probably do have other options, but why would you even bother?

I have no idea whether the lecithine will be helped by basic ingredients, but the results on taste will be terrible. With all that fat, you are likely to end up with the worst soapy taste ever. I wouldn't ever try going in that direction.

Do all these ingredients seem to be in the right proportion?

No. 15 eggs per 350 g of oil is very strange. Mayonnaise usually takes one yolk per 50-300 g of oil for taste purposes, although you can use less (books disagree on how much less, Ruhlmann's Ratio for example disproves McGee's On Food and cooking, saying that in practical tests, mayonnaise started breaking at around 1/4 tsp of yolk per 6 ounces of oil). I would say that 3-4 yolks for that amount will be normal.

The bigger trouble here is the water. While you do need a tiny bit of water to start a mayonnaise, if you add too much relative to the yolk, you end up with an ugly greasy soup. So you won't be able to make the emulsion first, then try to use it as milk. I have never used allulose, but I hope that as typical sugars it is water soluble, so you might have to create a syrup with it, then create separately your mayonnaise, then mix the two gently.

The whole idea will be very difficult to pull off. The mayonnaise will be doable, but thinning it with the syrup might prove difficult without it breaking. If you manage that, you have the next problem: I don't think that frozen mayonnaise is any good, I suspect that your ice cream will melt into a very weird and unpleasant texture in the mouth if you can get it to freeze into a usable consistency at all. And beside the texture, I expect the taste to also be pretty strange - more like an American sandwich sauce (you know, these sugared mayonnaises which you get in places like Subway) than like ice cream.

A much easier route might be to try making a gelato style ice cream by cooking a pudding with your water and sweetener and some starch, then mixing the oil (and eggs, if you want them) right into the cooked pudding. It is much likely to stand up to freezing in a machine, then thawing, although it is likely to taste better with much less fat than you are planning to use. Also, the problem with "sandwich sauce taste" will remain.