A couple of things I can help with although I have never actually stayed there.

Hotel Globo is in the centre of Portimao. From that point of view there will plenty of things in the city centre to keep you occupied in the form of shops and usual city centre stuff

It is however nearly two miles to the nearest beaches at Praia da Rocha. The little local public minibuses will get you there in a few minutes.

The riverside is OK on a nice day but I would not be so sure about the evenings. A great deal of the area is open space as it is often used for exhibitions etc. There are some restaurants etc near the bridge.

You can take boat trips up the river as far as Silves if the tides are right.