If this is for a tattoo, I would go with something shorter and pithier.
"Semper in Memoriam" -- lit. "Always in memory (of something)"
This intuitively makes sense to me, but I don't know if it's attested in any corpora.
Yes, your understanding is correct.
This is ablativus respectus, the ablative of respect.
If you look up this kind of ablative in your favourite Latin grammar, you will find examples, although not necessarily about differences.
If X and Y differ with respect to Z, that is expressed simply by putting Z in ablative.
The word order is flexible, and in some ...
My suggestion with complex sentences is always to try to identify the core and to rewrite it into a simpler independent sentence.
Here the core, as far as your question is concerned, has to do with ordering and loving.
Let us compare two descriptions of orders:
Te iubes amare.
You order yourself to love.
Te iubes amari.
You order yourself to be ...
Exempli gratia, how would one say 'I am perturbed' in Latin opposed to 'I am a human'?
I am perturbed = turbor or perturbor, if I am perturbed by someone or something in this moment (generally accompanied by a complement of agent). Otherwise, in order to express a condition or state, you can use perturbatus sum, where perturbatus is a predicate of the ...