Is co2 necessary and if so, what would be a good entry level system?
You can do low tech without CO2, but your plant choice would have to reflect low light. A good entry level system is really a pieced together system. An old victor regulator and minor parts is your best bang for the buck bet OR I've heard good things about CO2art.
Should I go with a pH meter attached to the co2 solenoid or do a timer? I’ve read about both and know I would need to regularly check the pH chemically if I don’t have a meter but with Bucephalandra would one be better than the other? I have a friend who will let me borrow his Reef Angel long term and this will apparently work for my purpose (plus other perks).
I wouldn't. Keep it simple. A solenoid and a timer is sufficient. You can dial in the CO2 based on the reaction of the fish and a simple drop checker, then it is set it and forget. Well, sorta. Monitor it periodically.
What kind of fertilizers would you recommend for this application?
Low tech? None or a modified EI dosing regiment. I'd go with EI dosing once a week instead of every day.
High tech? EI dosing and scale back until deficiencies are noticed and then bump the dosing back up to the last known 'good' dosing amount.
Would once a week water changes of 5 gallons a week be sufficient? I ask because I know it’s not 50 percent but would have to do this in 5 gallon buckets.
Simple answer: No. 50% is essentially a must do for EI dosing and high tech. If you go low tech, a 5 gallon water change once or twice a week is plausible with lower than average stocking.
I know very little about buce species, so I am just going off of general planted tank ideas.