To come back to the exposure:
With the Bolex RX-5 you have at 24 fps 1/65 if you not correct the Reflex system and 1/80 with correction. So your exposure time is lower then with other cameras.
You can also change the shutter as Gregg said, but be aware of the different motion blure.
You close the shutter a 1/4 if you put it on 1/2 and you have a corrected (Reflex system) exposure time of 1/122 and with 1/2 if you put it on 1 an exposure time of 1/188. But then you have not so much motion blur. You can also use it as an effect to see some water bubbles (I am not sure if it is correct English, sorry). This could be very nice!
I am sorry I am not familiar with north american weather at this time.
But I would expect with the normal shutter and the correction if the reflex system you have not more then a f11. And the wratten #8 needs a correction of 2/3 stop. And then you have a ND 0.5 with nearly two stops. So it should be no problem to shoot in this time of the year. We are not in full sunlight summer!
Yes if you want to have a deep focus then a f2,8 or 4 is good. But normally the best is at daylight a f5.6 and also with artifical light, but mostly you only have the change to have a f4 then. The deep of focus you normally should not controll with the aperture, but with the focal length, if you have the opportunity. If not, ok, then with the aperture.
But a f2,8 have other problems in the exposure, so try to be at a range of f4to f11 (better f8). And the depth of focus you will see through the viewfinder.
And do not be afraid of a bit overexposure. I know what others would say now. It is clear it is not a Kodak Vision, where two stops are not a problem, but 2/3 I would not worry. You can do more in a classical lab that many think today. (No I am feeling older then I am ;-) )
So do it! And do not think to much about this technical things! Do not forget your content, because of all the technical things!
I am sure you will learn a lot while you are shooting and the next time you have some expericence and it will be much better. As a filmmaker you are permanently learning...
Wish you all best!