". . . Or can I do it myself without any spanish language?!"
Cat, I concur with Whariwharangi. Pick a city east of Santiago from where you want to start walking, based on your plan to reach Santiago in 16 days. I’m assuming that 2.5 weeks does not include travel time to the start and return at the end.
Therefore, a safe starting point would be Leòn giving you a distance of 328 km (204 miles) to Santiago. According to
John Brierley’s guide, that would be 13 days with an average of 25 km/day (13 miles/day). It would also allow a day of rest and/or more time to climb the hilly paths from 1) Rabanal del Camino to Cruz de Ferro (350 m or 1150 ft elevation gain), 2) Trabedelo to O’Cebreiro (740 m or 2430 ft. gain), 3) Sarria to Alto Momientos (370 m or 1200 ft. gain), and 4) Portomarín to Sierra Ligonde (420 m or 1380 ft. gain). The rest should be a piece of cake.
If you decide to start from Leòn, take city bus 1A from Plaza Guzmán to La Virgin Del Camino to bypass the urban section on the west side. Plaza Guzmán is about 400 m (1300 ft.) west of, and across the river from, the Leòn bus station (Estacìon de autobuses de Leòn).
I just finished, arriving in Santiago on May 5, 2015 from Burgos. I did the St. Jean Pied de Port to Burgos stages last year starting on September 25th. The average daily cost was 30 to 35 euros based on staying in dormitories in municipal or private albergues. Add 6 to 8 euros per day if you have a baggage transport company pickup and deliver your backpack to your destination. If you have problems with the hills, or with muscles/feet/blisters, there are taxis that can take you ahead to your next destination. The manager of the albergue where you are staying can usually call a taxi for you.
I can’t say for sure, but I don’t think you’ll have any problem with finding a bed in September. The key is to reach your destination early in the day before they fill up. When you are traveling alone, you only need to find one opening. You will meet pilgrims along the way who walk at your speed, and they can help since they will also be looking for an albergue. You can do the Camino yourself without knowing Spanish. (I don’t speak any Spanish either.)
Re. Training: Be sure to walk 15 miles a couple of days in a row to verify that your shoes don’t give you blisters.
Best of luck on your training.