Hey Jeffery,
If you need it or not it would be definitely based on the type of design you have, your routing construction and the type of features you want to use. For example if you want to configure ECMP and have more than one Tier-0 as active then you will definitely need the Tier-1 as you will need them for configuring stateful services such as NAT, Firewall (Gateway) and Load balancing.
If you are only going to use NSX-T for providing L2 and L3 connectivity then maybe it is not needed but as i said it depends on how is the logic and the network construction you want to apply.
For going deeper in the configurations and recommendations i suggest you to take a look at the next document which explains all in great details even for the ones who are just starting with the product: https://images.nsx.techzone.vmware.com/sites/default/files/NSX-T-Reference-Design-Guide-Version-2.0_... . This is the reference design guide of the whole product not only for vSphere but also with KVM. Take into account that this document has not been updated yet to version 3.0.0 so for example you won't see recomendations of N-VDS vs VDS.
Finally and personal opinion is that today you have one tenant but if you want to grow in the future and there is a possibility of having more tenants or you think in a way of having multiple segregation i would go with a Tier-0 and then a single Tier-1. Doing that you will be able to scale on the Tier-0 is the throughput is desired and keep growing in Tier-1 (Tenants) as needed.
