This all looks very good.

To go on with the Starkiller Forge idea, which I think is fantastic by the way.

To reinforce this there is a scene in TLJ where Kylo and Rey have a force link conversation and Kylo has a hanger in the backdrop, I recall it looking like things are being built, AT-ATs and so forth. This may be a scene to steal from to add some depth to the forge aspect. Also, I like the idea of having Kylo and Rey having their mental link established in TFA. Pulling at least one scene and placing it in TFA would be cool. Also to that end, having Luke introduced much more in TFA is another one that I think would be neat. Push the destruction of starkiller forge to the beginning of TLJ in place of the normal opening TLJ scene you said you would remove anyway - the Poe run on the dreadnought. Incorporate elements of that scene into the starkiller forge destruction. The first order fleet with snoke went away to bombard and destroy Hosnian Prime, this was the resistance’s moment to sneak in and destroy starkiller forge. Some of this could be established in a new TLJ crawl.

Here is an attempt at a TFA crawl.

Hosnian Prime became the
seat of a New Republic set to
bring peace to the galaxy but
the galaxy is once more in
turmoil. Republic spies bring
news of a new threat.

Hidden from the New Republic
a secret order arose from the
ashes of the empire. Armed
with a mysterious weapon forge,
this FIRST ORDER moves to
destroy the New Repubic and
the Jedi once and for all.

Luke Skywalker mysteriously
disappeared. Whispers of a
failed academy, the Jedi Knight
is needed more than ever. The
New Republic create a covert
RESISTANCE led by General
Leia Solo…