There will always be a way to spent money. There was quite some at the first part of chapter 5 as far as I can see. Though you seem to have intel which is not implemented in the guides yet, because there is no 100k investment during the erosian war. So you've got to mean a ch5 investment (probably the one which is like the givini orc trader in chapter 4) but there is no information in the investments page yet. Is there more profit if [T - Erosia] is off?
Anyway the theltiar rentals have paid for 2 iterations at that point at the very least (3 times for me). Breaking even or not is quite a question of how many iterations we get in chapter 5 + they give hidden score too. Comparing that to - just for example - buying the mercenary flottilla is ... well, go bribe the bank instead of wasting 300k after 4 iterations. Though really I made sure to take all the important switches and save my money instead of going for the high end solutions (meaning I took -2 for ghant + the switch and kept the money). They tend to be not worth the trouble. In the end the fleet was the very one investment I didn't make for the very reason you stated yourself.
this is exactly what i mean for "money for the sake of money". having more money is pointless if i need to sacrifice some result. until i can gain all the best threshold there isn't any real need of extra money. for example, my army stats are enough to reach every best threshold during the war, so where is the point to gain more size or quality? if in the future more money are needed i can rework the playthough and perhaps lose some stats for strongh return, if the gain are enough, but until then it isn't needed and i aim for the best result everywhere.
and probably if i need a rework the first investment skipped will be Tak'Kan trade networks in the war aftermath. it's a lot of money and doesn't give any unique bonus (and Tak'Kan score isn't used before the vote during the vote in the erosia crisis section). i prefer keep it, but we will see.
the new dialogue with patrici increase airship counter (+1 if you fund the first, +3 if you finded the militarization too) and the new chapter 5 iterate event increase the counter as well. this strongly suggest the airship counter will be used in a future section, where, when and how are unknown, but it will be used.
for the investment:
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for the remaning return, in the chapter five research room there are a total of 10 researchs (7 accesible now, 3 behind the black sphere)
we have complete 5 projects [if your war don't result in a disaster] and one is undeway. this mean we will have with high probability at least 5 more iteration (read ProN return), perhaps six if will rise an opportunity working akind "qum project" in chapter 3. in the chapter 3 one can complete from 6 to 7 research project based on the recovery of aka spell during simon's route, in chapter 4/5 you can lose a research slot if your war end... not well.
i'm at the Ardan succession crisis at the momentbut don't really know who to Support.
I know Tyna don't wanna be a Queen. After Kalant saved her she has a crush on him. Sofar no Trouble.
Tyna want to support Ignias and that is a good enough Reason for me to Support him too.
Now what is if he want/ has to Maary Tyna? I mean she has Kalant which she has the crush wiith. And what if she would have enough Support and want Kalant as her prince consort ?
will be better if you don't weakened ignias position, his score will be used in a later section, and higher score is better. my advice [but it's only MY advice, we don't know the real effect of the scores] help kalant everywhere but ask min (if you fund her trade route) to works with ignas and tell to lynine to help ignias too and shot down all other cadidates, hard the better. [with farnan, you can be nice with him if your elleani rp are enough and you are senaky]. advice luanell to dump both candidates (if you can)