Max Ascension

In my opinion you should always ascend them but depending on materials for certain servants it might be more effective to wait until you enough for to ascend vital servants.

A less helpful answer is that it depends on the servant.
Since their stat growth varies there are several that has barely any increases in the last 10 levels while others grow the most at that point.
For others you need to max ascend them to do their strengthening quests, either to improve skills (Emiya archer) or even unlocking their final skills.

I think you can find the stat growth if you browse their pages here on gamepress. I'm not much of a help on that area.

Edit:
I eyeballed their numbers, approximate growth:
quetz 1200
cat 1500
helena 900
medu 1000 atk 2000hp
saberlot 300
emiya 1400

Conclusion: Except for Saberlot most have large growths and would improve by ascending. Helena could also wait since her true value lies in her skills.

In order to face Camelot, levelling knights classes should be your priority. Is your saber Lancelot, not my name right xd? He’s top tier saber. David is great however he’s kind of sub-DPS thus you might want to pair him with some nuke archers like Euryale, Robin Hood, Orion,.. then Emiya for rider boss and Tamacat to clear waves. I assume that you lack mats for Lancelot, Quetzalcoatl, Medusa because maps locked.

Therefore the order for leveling is : David, Nuke archers, Emiya, Tamacat > Clear Quests until Main Gate Quest > Farm medals for Lancelot > Clear Camelot > Farm Mats for Quetzalcoatl, Medusa at Babylonia.

Unfortunately with this order you’ll have to rely on strong friends in early quests. I suggest you to read “Spoiler-free Camelot quests”, it will help you to deal with those bosses alot.

I'd say that you need to level up your Servants a bit more before Camelot, maybe 1-2 more ascensions (my Servant selection is different from yours, so I can't say for certain, but I only felt comfortable with Camelot's difficulty level when my main roster were all lvl 70-80), but I don't think that max ascension is immediately necessary at least for the 5-stars. All my 5-star Servants are still at level 80 at most, and that doesn't feel like much of a hindrance.

Sad to say but, I really believe you should max Mash's skills and lvl her up to at least lvl 50 instead. None of your current team would perform well in Camelot at those lvls considering that ur resources are scarce. Quetzalcoatl's mats are only obtainable in Babylon. You're gonna rely on strong supports from ur friends.

As your only 4* support is Helena (and she's not really a full support), I wonder what your other supports are, or if you generally used a friend Waver. If the latter, I don't think you have enough damage to get through Camelot. Personally, my L65 Hans NP5 and L65 Georgios (who was in the backline for combat suit swaps for at least a 3 turn stall, and both with the 5* Volumen Hydragyrum CEs) were my mainstay supports. That allowed me to use friends max-levelled attack servants almost exclusively.