For me learning Portuguese after Spanish has been awesome. At the beginning, I did mix them up, but as you go through the process of learning Portuguese in more depth, you will make less mistakes. However, I will say that 2 things need to happen for you to be successful. You must have a reason to learn it and you have to have the ability or opportunities to practice it (through conversation). I hope this helps. I've absolutely loved learn Portuguese and Spanish is an amazing language too. I find them both to be relatively easy to practice.

I speak against myself, but I would not advise you to do so. A lot of cognates but also a lot of false-cognates. Besides, I would say that once you are very fluent in spanish it should take you about 2-3 months (or even less) to learn any kind of portuguese to a very high degree. However, if you are thinking about doing it anyway, I would recommend you to learn one south american variety and one european variety, as the fairly different sounds will help you not to mix things up. Note: Portuguese from Portugal has a lot of peculiar sounds and some foreigners mistake it for russian.

Aron, it's a good idea for a few reasons. The most significant reason, in my opinion, is that you'll find many things easier about learning Portuguese because of having already learned Spanish. Much grammar and vocab will seem like simply a variation on Spanish. But since you've already made in-roads with Spanish, the language learning process will seem easier with Portuguese, because you will already be familiar with the pit-falls as well as the successful times you've already been through while learning Spanish. (Your second foreign language is much easier than your first, and it becomes exponentially easier.) So the experience should feel empowering and momentum-building, as you realize you aren't just a Spanish student, but a language learner. Second, Portuguese can help Spanish seem easier to you, if only by comparison, since it is comparatively more familiar. After a few attempts at Portuguese conversation, it will be a relief to go back to Spanish, which again is good for you Spanish in terms of momentum, and new energy, and realizing that speaking a language isn't all that hard; it's as hard as you choose to make it. And of course, you Spanish will simply help you Portuguese, of course. In other words, learning Portuguese is easier for a Spanish speaker than for a non Spanish speaker. To summarize, the pros of learning both are that each language can reinforce the other, by way of contrast and comparison, and that you now get to speak with both Spanish speakers and Portuguese speakers. I can't think of any cons.

Usually a native speaker of Spanish need the doubbed of time to learn Portuguese than a Portuguese native need to learn Spanish. That happen because of the lack of the sounds in Spanish. Also how you know the Brazilian and the European Portuguese are differents. A lot of people find more easy to learn Brazilian Portuguese than European and one of the reasons it's the sounds. In beginner you can speak what people call Portunhol / Portuñol, but I think after some time and because they are similar it will be come easier, but in beginner you will have some troubles.