All solutions here are SUGGESTED. Mr. Teng will hold no liability for any errors. Comments are entirely personal opinions.
Order a list of all 5000 households from 1 to 5000.
Randomly select a number from 1 to 50 and taking that as a starting point, sample at continuous interval of 50. Eg, 10, 60, 110, …
Use simple random sampling within each stratum to obtain the sample.
Stratified sampling is more appropriate since it is more representative of the users of different age and shopping methods.
Some students overlook that for systematic sampling, we need to RANDOMLY select. For (ii), they can draw a nice table to present their answers.