You can apply an oil-based substance after applying vit. C (let the vit. C absorb first) but you should not apply oily substances prior to vit. C application because the water-soluble ascorbic acid will have great difficulty penetrating an oily surface.
I agree it is quite a hassle applying watery mixtures to the skin because it drips etc. I use a cotton pad, wet it with vit. C serum and basically clean my face with it.
The best way to get vit. C deep into the skin is to apply it after rolling with a 0.2 mm dermaroller.
Vit. C (ascorbic acid) is very useful for the skin but there are several challenges concerning using it topically.
Ascorbic acid is water soluble (not oil soluble) and as soon as mixed with water, the solution is not very stable. It starts to oxidize and eventually the colorless mixture turns yellow/orange color. You have to prevent oxidation by keeping it in an airtight container in the fridge. You should make a new batch about every 20 days. This is not a problem for homemade preparations but factory-produced ascorbic acid in water preparations would have to be sold and used within about a month, which is undoable.
That is why there have been many attempts to make ascorbic acid stable or using oil soluble derivatives of vit. C.
Using anhydrous mixtures - meaning water-free mixtures - solves the problem with instability of water mixtures but it has other problems.
As far as I know, one used method is to disperse a very finely grinded (micronized) ascorbic acid into silicone gel. When applied on the skin, the ascorbic acid will start dissolving in the moisture of your own skin. The silicone mixture is stable for longer than water mixtures and thus it can be sold in the shops.
There are other methods how to make ascorbic acid mixtures stable but if you are willing to make a new batch every 20 days, you do not have to worry about it. It is the manufacturer who sells vit. C ready to apply preparations that have to find solution to stabilize it because it can take a long time before the product reaches the customer.
Another way is to use oil soluble derivatives of vit. C such as Ascorbyl Tetraisopalmitate (= Tetrahexyldecyl Ascorbate).
Nevertheless, in studies regarding preparations of vit. C applied on the skin, the derivatives of ascorbic acid failed to increase the levels of ascorbic acid in the skin. Only ascorbic acid increased the levels of ascorbic acid in the skin.
“Derivatives of ascorbic acid including magnesium ascorbyl phosphate, ascorbyl-6-palmitate, and dehydroascorbic acid did not increase skin levels of L-ascorbic acid.”
https://http://www.ncbi.nlm.nih.gov/pubmed/11207686 Emulsifying wax is a wax treated with a detergent to make oil and water bind together. Yes, I think dispersing ascorbic acid in oils will reduce its penetration. You should at least grind your vit. C into a very fine powder.
Mild cases of sagging skin can be improve by a dermaroller but it can only affect the skin, not the underlying structures affected by aging such as receding fat and dropping down muscles.
I can't comment on whether facial exercises can slow down the effects of gravity and the general drooping of the skin’s underlying structures. I do not know.