I don't quite know how far you plan to take the "kitless" concept.
And, of course, making it a clicker is another challenge.
I think the suggestion to use the "Richard Greenwald clicker" is a good route. . But there are alternatives.
Some kitless clicker designs have been done with the click mechanism out of the PSI Slimline Pro kit. . That type of clicker mechanism can be bought, separately from any kit, on the website WoodNWhimsies.com :-
https://www.woodnwhimsies.com/product808.html
An example of such a kitless clicker is my submission (Pen Four) for the 2019 BASH Kitless Contest :-
http://www.penturners.org/forum/f422/2019-kitless-contest-vote-158721/
You, additionally, are concerned about threading the nosecone fitting. . I avoided that, in this particular example, by making use of tight friction fits. . However, I have done the threading by making the nosecone from two parts, one of which is glued into the pen barrel and is externally threaded on the other end to mate with an internal thread in the nosecone proper. . This additional step is not at all difficult if you use the right tools.
Please keep us informed of your progress. . As you can probably tell, I am quite interested in kitless clicker pens.