No need of any prebooking or any guide.As trails are well marked and you can get tents at top at Rs 400 per person.I visited there last month. For clearing all your doubts read my tripoto post on Parvati valley in budget.
When going to Kasol and if on a budget, you can trek to Chalal and find plenty options for decent and cheap stay. The trek from Kasol to Chalal will take 1-1.5 hour. In Chalal you have Cafe's like Fusion and Shiva which serve delicious food. For other treks you can go to Magic valley, Weichin. You can explore places like Manikaran, Tosh, Malana. There are many Cafe's in Kasol too, I would suggest you go to German Bakery as well.
Since you are travelling on a budget i would recommend you to stay in hostels and there are plenty of hostels in Kasol. I'm sending below names of a few you can look for
Whoopers Hostel, Nomads hostel, Gypsy Hideout and the Hostellers. For your accommodation in Kheerganga you will have to take your own tent or you can rent tent from Kasol as well. I'm sending with this message a posy about doing Kheerganga trek in budget. https://www.tripoto.com/trip/how-to-do-the-kheerganga-trek-in-under-rs-3500-586f57759c4ff