From fully automated Kiosks (an ATM looking thing that rents the unit, sets up auto billing on tenants bank or credit card, dispenses a lock if the new tenant wants to buy one etc), to smart phone Apps that do the same thing (except vend a lock) to 24 hour USA based call centers that will manage the business and rent the units for those customers who want a human to talk to (and the Kiosk software, smarphone App software, and call center sofware can all be seemlessly integrated within your business management software.

Most of the work is on the computer/smartphone.

A good camera or a new smartphone with a cutting-edge camera may trump the need for a laptop, but if you are seeking a laptop I personally like the Microsoft Surface Book - its lightweight, its got a touchscreen, it got a good battery and decent entry point for a decent machine. 

I have seen 5-6 smart phone companies.

I could maybe see an issue with exceptionally elderly tenants, who I would likely make an exception for, but nowadays, pretty much everyone has an email, computer and/or smartphone.

If your tenants have bank accounts and a smartphone, but have them pay you via Google Pay, Venmo, Apple, or straight out of their bank account into yours. 

If you haven't done so already, teach your contractors/handymen how to use their smartphones to their advantage to better communicate with you. 

I’d much rather have a 100 year old brick building with good bones (and updated electrical, appliances and plumbing) that was built by true craftsmen than a new stick framed house covered in glued together sawdust built with poor workmanship and controlled by smart phones but maybe that’s just me.

Before smartphones.

Those vendors have an RM app on their smartphones so they are alerted each time they receive a workorder from me.