Hi there, the weather in Barcelona & the eastern side of Spain should be quite pleasant with warm afternoons, however once you get to the South and through the Straits of Gibraltar, you should expect the temperature to drop quite a few degrees, the winds to pick up & more rain than sun.
Having said that, weather is weather, and whether is follows it's normal seasonal pattern is anyone's guess. I would suggest packing layers of clothes, along with a good waterproof jacket & brolly.
As for tours in Barcelona, if this is your first visit, then the hop-on hop-off buses provide excellent value tours to all the major spots and have headset commentary. There are 3 loops covering different areas of the city, you can buy tickets for any or a combined 3-loop ticket, either per day or for a 2-3 day pass.
Also I know a few people on this site have used local taxi companies (both for airport transfers & tours) & have posted the details here before, so hopefully they'll pick up your message & re-post them. If they dpn't then you may be able to find the messages using the search+ facility on the top of this window & look for the word Barcelona.
Remember that Barcelona is like any large European city, so hold on to your valuables, be wary if approached by strangers, and stay in the main well lit parts of town in the evening.
Hope this gives you some help,
Alan & Katrina
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