Hola - welcome to the forum. Your questions:
1 With 45 - 50 days you have plenty of time. In all probability you will reach Santiago in under 40 days (or less
) giving you the option of walking on to Finisterre/Muxia if you wish. With this timescale you may also wish to linger in cities or other places along the way.
2 The common advice would be to do at least some training/practice before setting out - walk with the shoes or boots you will use and with your rucksack packed focussing on trying to get it as light as possible. Walk at your own pace for distances with which you are comfortable - your stamina will quickly grow.
3 On the
Camino Frances you won't be alone for long. Setting out from St Jean at the end of September there will be plenty of other pilgrims on the way.
4 Weather - who knows? Walking in October I'd have good rain gear and clothes that I can layer as it can be cold in the early mornings and late evenings. I'd also be prepared to buy sunscreen
Look at the long range forecasts before you leave. I would not expect extremes of weather at that time of the year.
5 Accommodation - the albergues will still be open end of September beginning October although progressively some start to close for the season or to give hopitarleros a break or for work to be done. I set out from St Jean on 11th November three years ago and there were enough albergues along the way to satisfy demand - there are more now! My advice would be to take each day as it comes - there is no need to plan ahead any more than the day in front of you. In my experience of winter walking the albergues in Galicia (from O Cebreiro to Santiago) will be open and heated. Take a guidebook with details of accommodation if you wish.
6 For someone young and mildly fit (you will be by the end!) the
Camino Frances is not inordinately strenuous - it is also very safe. In saying that all normal rules about personal safety and the security of your belongings apply.
You will be leaving for St Jean in around 4 weeks. Have fun preparing. Take as little as you can - light is good!
Have a wonderful camino and please let us know how you get on.
Buen Camino
John