Hi - retired male TA here -
Yes, I would agree with the other replies, there really isn't much to worry about!
I worked in primary schools in various capacities for over twenty years, and although children may come in to school with a variety of pre-school experience, or non at all, or come into Yr1 or even Yr2 having had virtually no previous formal learning, they do all make adequate progress in the end, though some will take longer than others.
A major factor is the amount of support and parental involvement a child receives at home; unfortunately some parents think it is ONLY school's job to educate a child, and they play no part even in supporting reading at home, but these families are a small minority, and would not be MN members!
Many Yr1 classes do not spend VERY much time at tables, or desks! A lot of the time children will probably be on the carpet, in the hall, in the computer suite, in the playground, the garden, the art & craft area, or whatever. Obviously, the larger the school the more areas and facilities there will be for different activities.
Very likely children will sometimes be encouraged to work in small, independent groups, or discuss ideas and maybe 'feed back' to the rest of the class. Confidence and ability to talk, share and take turns is therefore a valuable skill. Also confidence to 'have a go' at sports, games, PE, music, drama etc, is useful.
Perhaps I would advise you not to be TOO specific in telling him what to expect, just in case he perceives things not to be what you promised him they would be, and feels you misled or 'tricked' him. Security and confidence are very important, particularly in the first days and weeks of being in a new environment.
[In a day or two I will try to 'message' you with some excellent 'links' that you can look at together during the holiday, and some information to help start you both on the Literacy & Numeracy road. There is, of course, plenty of informal 'education' on BBC TV and other children's channels]