I wouldnt use the 45 CT1 on 5Dmk3. The trigger voltage as I read it is around 400volts and if the serial number is below 534000 it can ve as high as 600V. Canons official line re: trigger voltages is (or used to be) 6volts max but that was for early series DSLRs (300d/350d). The newer line of DSLRs (your 5Dmk3 for instance) are rated to a max of 250volts. The information re: the CL1 claims 6-8 volts and should be okay. The above is assuming use in the hotshoe. Firing via the PC sync socket which is more tolerant to higher voltages, but possibly 400-600v!!! is a whole other subject and I would reccommend against it with the CT1 without further investigation. There are adaptors available (Wein Safe-Sync) which can reduce these high voltages to safe levels but it is it really worth it to use an old flash (Manual only too, E-TTL will not work) on a $2000 camera ?
https://www.bhphotovideo.com/c/product/245292-REG/Wein_W990560_Safe_Sync_Hot_Shoe_to.html
http://www.botzilla.com/photo/strobeVolts.html
A lot of older flash units for film cameras wont work on digital cameras. Old flashes dont have compatible electronics for modern digital cameras. Flash sync is a normal issue. Try setting the camera shutter speed to 1/60 or 1/100 and try that. The trigger voltage may be too high. To use the sunpak 555 you will need the TTL connector to the multiple contact points on the hotshoe. It might be cheaper to get a remote slave for the flash and use it off camera as a small studio flash. http://camerapedia.wikia.com/wiki/Sunpak_555
Hi
I am not familiar with the 30D but there is a parts list shown here:https://elektrotanya.com/canon_eos-30d_parts.pdf/download.htmlWhether you can get the parts is another issue. You would have to try and see if Canon can still supply in your region.I hope this helps.
You need to use triggers, one on the hotshoe and one on the flash gun. Unless you're using the most up to date compatable kit have a look at Younguo triggers on Amazon
I don't think you can as far as I'm aware the camera downloads to both cards or one card. I don't think there is the function to fill one card then move over to the second card.