It's easy to get a taxi from PDX to downtown, there is also the max, which is a train. Public transport in the city is not too bad, there's a tram plus buses. There is a big issue with homeless camps. But I like the city, it's edgy and a bit different to other US cities.
Portland has a great food and coffee scene. Check out the food carts / pods, loads to choose from and cheaper than restaurants. The Japenese garden is very cool. And I love Powell's, the world's largest independent bookstore.
Washington Park has lots of great trails for hiking and you can get great views of the city from Pittock Mansion. The Zoo and Omsi are fun too. Spring is beautiful in Oregon! But it may still be quite wet, so come prepared for that.
The Columbia River Gorge is well worth a visit and only about 30 minutes from Portland. Multnomah falls is good but v crowded. There are lots of other waterfalls to see along that route. Go to vista point for great views. We also really like Hood River, it's a cute town right on the Columbia River.
Further afield, the coast is wonderful! Also Silver Falls State Park is great for hiking and seeing waterfalls.
For shopping, visit Woodburn, it's a big outlet mall about 1 hour or less from Portland.
And a visit to Mount Hood is a must. In April there will still be quite a bit of snow so you can ski or go to a sno park to sled/ build snowmen.
It's about an hour from.the city.
You'll have a great time! If you want to come back when it's warmer/ drier, September and October are great months to visit as its also not as hot as the summer.