What is the nitrate level in your tap water? In order to tell how much nitrate has been made by the bacteria, we need to subtract the tap level from the tank level.
The fish that will be arriving - are they enough to fully stock the tank, or just the first few?
The trouble with using fish food as the ammonia source is that you can't know just how much ammonia they make. When using ammonia solution, enough is used to get an ammonia reading of 3 ppm. This figure was chosen because it grows more bacteria than a fully stocked tank needs but is not enough to cause the cycle to stall. But with fish food, how many bacteria have grown? For this reason it is advisable to add fish a few at a time rather than all at once as when using ammonia solution.
As you have been cycling for a month, you will have some bacteria but depending on how many fish will be arriving, you may not have enough. But there is something you can do - buy a lot of live plants if you don't already have any. Plants use ammonia as fertiliser and they don't turn it into nitrite or nitrate.
Probably the best plant would be water sprite. This can be planted in the substrate but also makes an ideal floating plant, and floating plants take up ammonia faster than most plants lower down in the water (simply because they can get carbon dioxide from the air and they are very near the lights, both of which are also needed for good plant growth).
To your question:
Buy live plants as soon as possible. Floating plants are best followed by stem plants. Plants such as java fern, anubias, moss balls are slow growers which won't have much effect for a while, so don't get those.
If the fish due to arrive next week are not the full tank's worth, let them come. Test the tank water every day after they arrive and whenever you see a reading for ammonia or nitrite above zero, do a water change.
But if they are the full tank stock, delay them. Even if you buy a lot of live plants they may not have settled in and be growing well enough for a full tank of fish by next week. Once you see new growth on the plants, then arrange redelivery.
If you don't want live plants, delay the fish, buy a bottle of ammonia solution and follow the instructions for fishless cycling (it's a sticky in the Cycling section of the forum). Since you'll already grown some bacteria the cycle will go faster but at least by the end you'll know for certain that the tank has enough bacteria.
If you have the possiblity to get Seachem's Prime before your fishy delivery, you can put your fish in with no worries doing water changes every two days until your ammonia and nitrite levels remain at 0ppm for 7 days.
