I understand the feeling that having someone look after the logistics for you seems safer, but I also agree with those who say it is really just as easy - and sometimes more comfortable - to do it yourself. Book your own flights to suit you. Get a good guidebook (look at the ones Ivar is selling in his forum shop), keep training. When you have a guidebook in your hand and a good feel for how far you can or want to walk on flat or hilly terrain in a day, have a look at what accommodation will be found there. Guidebooks like the
Brierley guide, which I have and use, will suggest daily stages for you and list suitable accommodation there, and you can find many of these places on booking.com to book youself without having to make phone calls in Spanish. No need to book it all right now, but I would book the first two nights and the last one in advance. When you are actually there you might want to take a day off, walk a half day because you meet up with someone or find a place you want to explore ... you can't know that yet. Jacotrans and Correios are good bag transporters and very easy to arrange day to day, so as soon as your boots hit the ground you will have unlimited options, while if you get someone to organise it for you, the itinerary is locked. I am not saying don't do it, I am saying give it a good think - you can do this on your own.
Also you could go to Leon to see the city and rest up after the journey, and still go to Astorga to start walking (I am a firm fan of a two week walk from Astorga - beautiful scenery, good infrastructure, long enough to get into camino mode). Even if you do decide to go with a company, I would recommend getting a normal guidebook and double checking the distances and climbs etc and not just blindly follow someone else's itinerary. I am only saying that because we met a lady from Australia who had a spiral bound self-guided book that told her to walk 40km on tarmac and steep hills one day and 10km the next ...
If you would like to consider it before you book through someone, feel free to send me a PM and I would happily help with stage and accommodation suggestions based on my 5 walks on the Astorga-Santiago stretch. Buen camino!