I have bolded the items that I would like you to elaborate on, as I feel I did not understand them quite well.
1) There seems to be reason to believe that in the past, the letter now written and spoken in standard Arabic as /q/ was commonly pronounced as /g/ (or /G/). I suppose you are perplexed by the fact that the letter now realised mainly as /d͡ʒ/ used to be realized likewise as /g/ at some point, as clearly shown by semitic cognates (and by the realization in Modern Cairene spoken Arabic, where it seems to be a retention).
It seems that there this is explained by dialect difference within pre-islamic Arabic; in some dialects /g/ became /d͡ʒ/ and in a subset of those at least, /q/ became a new /g/. This situation was widespread and probably considered the standard prnounciation at some point. But later (perhaps in the ninth century) the standard was defined as having both a /d͡ʒ/ and a /q/ sound, but no /g/ sound. This is possibly because the /q/ realization was seen a feature of "urban" speech while most Bedouin speech form had /g/ (as shown in Iraq by the oppostion between the so called "gilit" and "qelti" varieties - from the respective voices for the perfect of the verb "to say" ("qult-"/ in Standard Arabic).
2) I do not understand what you don't understand about lexicon. I said that if this language is Romance on Arabic substrate, the number of Arabic lexical items that enter it is likely to be relatively low.
3) Semitic languages have a distinctive (and very discussed) root-pattern system. Essentially, the basic meaning of the word is conveyed by a primarily consonantal root, normally composed of three letters. These are arranged in fixed patterns with infixes (usually vowels) prefixes and suffixes to articulate meaning and inflection. Textbook example: "darasa" = "he studied", "yadrusu"="he studies" "durisa" = "it was studied" (by unknown agents), "yudrasu"= "it is studied" (by unknown agents) "darrasa"="he taught" (made study), "mudarris"="teacher", "daaris"="he who is studying", "madrasa" = "school" (place to study), "dars"="lesson", "duruus"="lessons", etc.
This system is also sometimes extended, through reanalysis, to loanwords (for instance "film" has a plural "aflaam").
This is not a feature that could be passed into Romance by the substrate, but I was saying that there's a possibility that some residue of reanalysis on the root/pattern lines can show in alternances where the change of the vowel sound in a root signal a shift in meaning (this is something that occurs in Indo-European and was hugely productive in the pre-history of Latin, but not very productive in Classical Latin anymore).
4) Arabic does not a verb for "to have". Latin did. This verb expanded greatly its function in Romance, coming to be used as an auxiliary verb, in roughly the same way it is used in English and in German.
A Romance language with an Arabic substrate might not have the same development, and instead lose the verb entirely. In that case, its verbal system would differ from the other Romance system as it would be using the equivalent of "to be" as the primary, if not sole, auxiliary verb. The verb "to be" is the only auxiliary verb in Classical Arabic.
I also argued that other auxiliary verb may develop, especially to signal the future (or continuous, etc.). This is what happened in spoken Arabic, in some Romance languages (Italian uses "to come" as an auxiliary for the passive, Spanish and Portuguese developed "to stay" and "to hold/have" as auxiliaries too, etc., so this sounds like a probable outcome).
I am sorry if this sounds still unclear.
Also, I think that I mean Classical Arabic in this case for the purposes of ease,
Technically somewhat inaccurate but certainly justifiable on the basis of ease, yeah.
Furthermore, I would like to say that I am inexperienced, but judging from what you've said, I decided to do a really crude transformation of a latin phrase, and I would like you to tell me how I can improve it. Also, I did it in (again, very crude) IPA transcription, so if there are errors in that, please tell me.
Here is the phrase
entia non sunt multiplicanda praeter necessitatem
[IPA: ɛntiɑ non sunt multiplicɑndɑ prɑjtɛɾ nɛkɛsitɑtɛm]
Here is a really crude transformation that I'm guessing at with what you've told me. It is most certainly horribly wrong, because I am not at all well-versed in any arabic, but I'm trying to create a starting point.
[IPA: non sunt multəfləcɑndɑ alkjənɑtɑ frɑɛtur xtɑgɑ]
I do not understand why you chose to turn "entia" into "kjenata". Are you using the Arabic root for "to be"? It is unlikely to survive in a Romance version I think. While Arabic "xtaga" is a reasonable loanword. For the rest, not bad.
As I said, I don not believe the final language will preferred VSO order, but it is not impossible either.