Re @Cassius' feedback :
SOE19: Friendship is necessary for securing happiness. It is advantageous to promote Epicurean philosophy in order to widen our circle of Epicurean friends.
Objection to SOE19: As just stated in relation to 18, it is perilous to imply that "friendship" as an abstraction is necessary for happiness. The Epicurean texts are clear that everything is contextual, even friendship, and this statement is not contextual - no individual example of "friendship" or any particular "friend" is stated in the Epicurean texts to be across-the-board necessary. The second sentence in this tenet seems to me to clearly be true, but it is a much more narrow statement than the first sentence.
I changed "friendship is necessary" to "friends are necessary" - in fact I've observed before that using the plural tends to help take concepts from the abstract to the concrete. Tenet 11 establishes the telos clearly, this Tenet has nothing to do with the telos nor does it state that friendship is the telos.
The LMenoeceus says that the natural and necessary goods are those that we need for health, happiness, or life itself. There is research that demonstrates the bodily health effects of isolation, which are compared to obesity and smoking. Then there is also the problems of MENTAL health, which are much worse, and affect the category of "happiness". Therefore, it's clear that friends are a natural and necessary pleasure.
Further, concerning the natural and necessary pleasures and this feedback
SOE17: To live pleasantly, we must have confident expectation that we will be able to secure the chief goods: those things that are natural and necessary for life, happiness, and health. Therefore, whatever we do to secure safety, friendship, autarchy, provision of food and drink and clothing, and other basic needs, is naturally good.
Objection to SOE18: "Chief goods" is not a term that Epicurus employed and implies that there is an outside ranking of pleasure which does not exist. The natural and necessary observations are helpful for analysis because it helps us consider the result, but WE weigh the result and make our own determinations of how much pleasure and pain is worthwhile - nature does not do that for us and there is no uniform rule established by nature. All of the things you have listed (especially / even autarchy and friendship) are tools that are generally useful in the pursuit of pleasure, but for every single one of these there are going to be times when we forgo or avoid these in our own pursuit of pleasure. Even food and water are to be avoided when fasting is necessary for survival or better health; air to be avoided when holding one's breath to escape danger is necessary; etc. And so it is explicitly wrong to imply that such things are "naturally good" in each and every circumstance. The only thing that Epicurus said is **always** desirable is pleasure itself, which is the result of activities that are themselves always contextual and sometimes to be chosen and sometimes to be avoided.
This, again, says nothing of the telos, nor does it replace it, nor does it state that the telos is replaced or abrogated by this. The doctrine on the telos is articulated clearly in Tenet 11. The natural and necessary pleasures are what Philodemus calls "kyriotatai" or chief goods in the Choices and Avoidances scroll--where he is adamant that not knowing how to separate these from vain desires. Here is his quote:
Column V. For men suffer the worst evils for the sake of the most alien desires which they take to be most necessary–I mean desires for sovereignty and … reputation and great wealth and suchlike luxuries … they neglect the most necessary appetites as if they were the most alien to nature.
Column IX. Many and great evils concerning many matters occur as a result of the worthless assumptions of mindless men and are avoided as a result of the right concepts.
So here he is making the point that it is important to keep in mind these chief goods and to never neglect them while going in pursuit of vain desires.