1) where should i start the Santiago if i'm looking for a simple and easy route?
2) using a tent, is it doable? what routes will provide better terrain and weather to use a tent?
3) what should the weather be like if we're talking about starting in jul/aug ?
1) I think your confusion stems from the idea that there is a simple, easy long distance route
to Santiago when in fact there are about 20 different routes, some shorter than others, some easy and some difficult and some with a mixture of both. You are an experienced hiker so I'm sure you know that if you walk over 1000km across a country you will encounter easy - difficult - and everything in between! Most of the longer routes cross mountain ranges, different climate zones and have both flat and easy, and hilly difficult sections. I would say, walk the Camino Frances
- the most popular route but also the busiest and can be very hot and crowded in summer.
2) You could probably use a tent throughout France and Spain if you wanted to - but you might not want to in the higher, colder places or places where you have no access to water or food. In some built up areas there might not be anywhere to camp wild and camp sites are often more expensive than staying in a refuge or albergue as they charge for you and the tent.
3) End of July and August are the busiest months (European holiday season) and the hottest so you will have to factor that into your plans as well. The Camino Frances
in the north of Spain doesn't get as hot as the Via de la Plata (over 40oC in some sections).
If you find time on an internet, it might be worth looking at one website - http://www.csj.org.uk
- where you can read overviews on all the individual routes to Santiago.
If your girlfriend hasn't walked more than 2 days in a row she might find a long trek like this really difficult. Is this really what she wants to do? If so, she still has time to start training.