Shrew
AM
No more splashing in the shower preferably, dry/dehydrated is fine to go without cleanser in the morning but just splash with not too hot water (it's drying) at the sink, please 
Try patting the Vit C in instead of rubbing, placing three small dots on your finger tips and pat in gently but quickly, at least till you get to the end of it. It's the best way I've found it to work and to leave it alone for at least 30 secs after applying, I usually brush my teeth or something. I would not DIY with Vit C, it's too tricky and unstable and the initial layout is quite pricey. With your budget concerns I'd try the Nufountain C20+ Ferulic Vit C from amazon.com (not uk), $26.99 (shipped I believe for that price). Keep it in the fridge to preserve its potency as long as possible.
Olay serum - if you're not having issues using this and TO Vit C together continue as you were, but the high Niacinamide content and Vit C are contraindicated by TO, but as mentioned before the science on this is iffy.
eucerin cream,
biore watery essence SPF
I'm assuming both of these ^ are working well for you? Dulci (also dry/dehydrated) and I (normal/dehydrated) are both enjoying the Benton Snail Bee High Content Steam Cream which is great on the occlusive and hydrating front if you need an alternative. Dr. Hauschka Rose Cream if you're in need of something heavy duty to combat dryness (not too strong on hydration.
PM
Emma Hardie balm, < I'm still waiting to hear from Hollin what it's like but I think the Heimish All Clean Balm could be a viable alternative (it's around US$15 shipped) but so is the Body Shop Chamomile Sumptuous Cleansing Butter at £10 and usually there's a discount available.
Since you're not using base makeup and the Biore is a wash off that isn't sweat/water proof I think single cleansing is fine for you, esp. considering the dryness.
alternative nights retinol (was skinceuticals, just started trying TO 2%)
and other nights Olay serum then < there's no issue of using this together with the retinol, as long as it layers well I'd use these together or add in the Vit C on retinol nights (use before retinol), Vit C helps boost the efficacy of retinol (also SPF but I'd stick to using Vit C once a day).
TO Argan oil < I'd add in moisturiser here, before or after oil (and I'm assuming you use this every night) or drop in the oil in moisturiser, you can do this in the AM too for the dryness.
Things I'd think about adding in:
An extra hydrating serum AM/PM like TO Buffet
Acids- prepare to not be surprised I think it's worth trying BR P50 because it is that transformative. Pricewise it isn't the cheapest (can't recall the price in GBP, if someone can help out with that) but the 50ml travel size lasts for well over 6 months (mine is yet to finish, it's been 7 months and I've given out two decants) to use on the nights you're not using Retinol. Just for clarification what were the issues with the acids you tried?
You can consider phasing out the Olay Serum and replacing with the TO Niacinamide 10% and when Aurora (also dry no longer dehydrated) can form some proper feedback on it the TO Matrixyl.
Possibly invest in some oil blends, I know this gets expensive but if you're dry oils are the place to invest your money and the single straight blends tend to under-perform in comparison.