Jerome should be the first thing you awaken. Due to his skill not changing, and his cost, Ive found he's worse CC'd than Pre-CC'd due to the 3 extra UP to deploy him when his main role is generating more UP. After Awakening however he is better due to the +2 boost to starting UP.

For more short term gain, awakening Elizabeth is good given she is generally a good unit, and it lets you increase her max damage as well as increasing her range.

That said, if you are looking at long term strategy, I would personally suggest prioritizing Cellia (for better spirit drop rates), Monica (for better DC drop rates), and as an eventually (though lower priority than more useful combat units) Cuterie (for better gift drop rates, though provided you aren't trying to max affection every girl, instead just focusing on those you use, you likely don't have too many issues with running out of gifts).

As for other useful units to awaken in no particular order:

Saki, if you use her. Ninja presently get a -4 cost reduction on awakening (eventually a patch will reduce their normal cost by 2, making the awakening reduction 2 as well, but until then...), and in her case she also gets a faster attack speed, making her much more useful. That said, if you don't use her much it's likely not worth it.

Odette will be handy to awaken as what looks like your primary mage. Mostly, due to gaining more damage helping to more quickly take out groups, though her increase in MR may occasionally also be handy.

Len might be useful, as noted she boosts everyone's defense by 5% and when you use her she will reduce the skill cooldown timers even more than before awaken. That said, I've personally not felt that I needed to awaken her but preferance may vary.

Claudia is quite handy to awaken as a princess and likely one of your better Duelists. Her true damage skill may prove quite useful in the future, and she has fairly good stats beside. Awakening will just make her better.

Iris is a good pick as a healer. Awakening her will cause her to heal everyone when deployed (something I actually used to 3* Danger in the Oasis as to prevent the early group of axe throwers killing my units before they could be dealt with, though admittedly I had a mine min-costed as well). Admittedly you already have the platinum healer awakened who has a stronger version of that ability so it may be a slightly lower priority, and you may potentially get more out of Fedora.

Bernice is a rather good tank. While you do already have an awakened Gellius, eventually you should awaken her as well. Not only is her defense only slightly lower than Gellius, she also increases the defense of all Heavy Armours by 5% just by being in your sortie.

Fedora. While I don't use her, having already leveled Iris enough and having some other better healers as well, she does have a higher non-skill heal at max level, and her awakening reduced her UP cost by 1, making her faster to deploy. Additionally her range increase skill may be useful in some situations.

Cloris or Yuyu would be useful to awaken, due to filling the role of a ranged magic damage dealer. My personal preference would be Yuyu, as she has notably higher base damage, can be CRed and awakening further lowers her cost by 1. That said, Cloris has better burst damage with her skill, and does gain a low chance to instant kill enemies when she hits them (not really enough to be relied on, but it is a potentially nice benefit)

Katie may be nowhere near as good as Jerome, but she is still useful, and her awaken ability gives everyone +2% defense if she's in the sortie. Not a high priority, but potentially worth doing eventually.

Outside awakening units, you also seem to have duplicates of some units you seem to use. While it ultimately is up to you, it likely is worth using them to CR/Skill up the copies you are using, though I would note in advance that eventually when rainbow crystals are introduced, you can gain them by discharging higher rarity units (and then spend them to get some very nice units from the trading post), so if you don't feel the chance of a cost reduction is worth it, it may be better to save them for that (to clarify, the units you can get cost 1000 rainbow crystals, while non-event platinums give 100. I forget how much other rarities give, but high rarity provides more). I would note though that in the case of Cellia and Fedora, it may be best to wait until after awakening to combine them so as to gain the experience as well.