When are you flying? Right now things are ok, but come summer - it will be chaotic again.
There are many flights that come in early in the AM and you may end up having to wait 30-60 minutes to clear passport control, though as I said - winter tends to be better. 3.5 hours is definitely enough time to get through passport control and enjoy some time in the lounge.
Once you pass passport control you have to go through security and then on to the lounge. After the lounge - you go directly to your gate. If this is a single ticket - bags will go all the way to BCN.
If you get through passport control within 30 mins, you can grab an uber/cabify/taxify to the center or to Park das Nações and get a coffee and a pastel de nata (or whatever suits your taste). It shouldn't be more than 6-9€ by uber to the center, and takes around 15-20 mins. I would grab an uber in the center about 70-80 minutes before your flight, though in a pinch you can leave the city center an hour before and still make it without many problems [been there, done that, numerous times].
If you decide to stay in the airport, and bought a pass for the ANA lounge and want to take a shower - bring a towel, otherwise it's between 10 and 15€ for the shower kit (the shower itself is free).