In CMA for every one moment of rūpa, 16-17 processes of citta occur. So they are not totally equivalent.
Correct and this actually strengthens my point. The Atthassalini says time is mind. So the change of rupa is imposed on it due to cittas activities, the same goes for the maturation of past actions in present forms. You have to see that rupa can neither change itself due to the absence of cetana, manasikara, vicara etc. but that its also not hetu and its ahetuka (see Kathavatthu XVI).
It might also be relevant to note here that in Theravada rupa is not vipaka. Eventho the sense-bases for example are said to be vipaka its actually not the bases but the cittas who reflect / project these bases. Thats a very important point imo. (Ibid.)
Take cohesion for example. Cohesion is a rupa but it can neither change in any way nor can it interact with any other rupa. How should it? It does not have a spatial location, does not have a temporal lcoation, it does not have a direction, it does not have the attribute of being able to take an object and so on and so forth.
It follows that rupas can never show up without being the objects of cittas.
Five sense objects are object Pre-nascence-condition (ārammaṇa purejāta paccaya) condition for 5 sense consciousness. They exist prior to consciousness.
As said above Theravada is ksanikavada and present-only. Every transformation of both citta and rupa has to be explained therefore as a sequential, singular appearance of entities which necessarily have to build a continuum (santati) with the death of the earlier dharma directly conditioning the birth of the next dharma. So followingly rupas have to be in a citta-santati to have apparent causal efficacy.
In addition as said above the sense-bases are karmically produced, so they do have a mental cause.
3) rūpa can exist without consciousness happening at that time. Ex: asaññasatta, saññāvedayitanirodha, dead body.
Actually for example the Yogacarins have argumented, that - since Theravada is a present-only school - that it is impossible for an Arahant in Nirodha to come back from it, because the continuum is cut off. As far as I know this is a hole in Theravada philosophy. A bit earlier Nagarjuna argumented in a similar way [from the Sarvastivada pov] explaining that a past cause is an inexistent cause and therefore a non-cause. I am unaware out of my head if Theravada answered to this in a more elaborate way.
And again you have not answered how body can exist without consciousness (when one dies, or achieves cessation of perception & feelings, or mindless beings rebirth).
The latter I have explained given the standard "quickfix" which is admittably not logical - but thats how it is.
The second one and first one are misunderstandings I think on your part. "Dead body" is a sequence of smells, visibles and so on in another mind-stream. There is no indication that there is a dead body apart from mentality anywhere - why? Because if there would not be any consciousness then there would be no temporality or locality and followingly also no "dead body".