If you are " just building base" then you don't need any special equipment. A heart-rate monitor would be helpful, but it's perfectly possible to work on perceived effort.

The basic principle is that you should mix it up. The bulk of your time on the bike should be long steady distance (LSD) riding. If you can organise your time to allow you one ride of five hours once a week that would be good. Do it at an intensity that you can maintain, but don't dawdle. You should be tired, the last hour should be hard.

The rest of the week should consist of rather shorter rides. One or two of them should be a bit more intense. No need to immediately start intervals if you are base-building, but at least one ride of about an hour at the highest pace you can maintain for that time is a good idea.

Rest a couple of days a week. Schedule your rest days after your hard days. And when you are on the bike, make the hard days hard and the easy days easy. The latter is the difficult bit, most people go harder than they should on their recovery days. As a result they don't recover properly, stay tired, and therefore can't go hard enough on the hard days.