Re: (Nutaku) Milenium War Aigis (English Version)
In general units with high unit cost gain not as much from CR as lower cost units like soldiers, valkyries, front or rear guard strategists.
See it that way: Marius costs either 35 UP or 31 UP (min cost + Olivie). That does certainly make a difference on some maps. But: Both values are pretty high and therefore you are not very likely going to place him early on a map. Usually you'll place those expencive units towards the later stages of a map: The part of a map, where time, soldiers, valkyries and front guard tacticians generated so much UP, that it doesn't matter that much whether he costs 35 or 31 UP.
Other units, like soldiers, valkyries, front guard tacticians, rear guard tactivians, maybe even rogues... in general units that are more efficient the earlier you are able to place them, gain much more of cost reduction.
Therefore Aisha is a good choice (besides her being OP). Since Mikoto is so strong and can buy you time with her skill, she is a good choice as well. Sophie not so much. Overall a good unit, but mostly used as a lightning rod, so in most scenarios you won't be in a lot of UP pressure when you want to place her.
Iris is certainly useful, but risky. The chance for her last CR is 25 %. Most of the time it's probably a better choice to pick a safe CR (first CR is always 100 %).
Katie... Honestly, there are better secondary soldiers beside Jerome. Depending on the futire handling of Revivals events and there frequency: The second to next revival event will feature Aria. In general more useful stats, ability and easier to CR. If you get her your CR on Katie will probably prove useless.
I'd give Jerome at least one platinum bond fairy btw.
As for the replacements: Bashira vs. Spica: Depends on your preferance and the reason for your question. Are you asking for the future or for your current units. Because in your current units I'd keep Bashira and replace Soma with Spica (and Daniela with the Elizabeth I know you have).
As for Marius: It doesn't really matter whether you use your platinum bond faries on him or not: In both cases he is a lot better than Valeria and as previously stated in most cases, the cost difference doesn't really matter (and if you want a cheap mage: Pick Pallis over Valerie).
Now Adele: Pretty much what Sashas said. She is great but not that useful to you.
