Down here in the Algarve it will be around 85 - 90F so not that much different to Orlando as I recall from my one visit there. The sea breezes along the coast do keep it from feeling absolutely oppressive, but a lot of people cannot do without air-con. Even 50 miles inland it can be much hotter, no wind and semi-desert conditions prevail as you head north into the Alentejo.
If you want a quiet time of it, the Algarve may not be for you. The region is one of the most popular destinations for holidaymakers from Northern Europe and indeed Northern Portugal, so in July and August everywhere (we hope) will be packed.
The north-east is quite mountainous and quite a bit cooler in summer than the south and Alentejo but still very pleasant. (I go there in October or November when it always seems to be raining!) It's much more authentic up north that the golf courses with their glass and concrete resorts down here. There are still several beach resorts for a change of scenery.
As for car hire, all the major companies are represented at the Porto and Lisbon airports. It's just a matter of going to their websites and checking the prices.
As for that website, I cannot see it should not be reputable but perhaps you can search on Trip Advisor and elsewhere for reviews and testimonials.