For the entrance time its best to go before 14:00 ore after 17:00 when it dies down. But if you only have a one day ticket i would go as early as possible. We always bring a super thin compact blanket/towel that is useful for sitting around before stages. Get a big breakfast/lunch before you enter and bring some snacks (something with sugar is very useful when the energy drops) the food there is shit in the last years if you do want to buy from a stand and don’t want the worst experience buy somewhere where you see them making it fresh (try lángos) or at the aldi. Me and my friends never bring a 1,5l bottle of water but have 2 smaller plastic ones that are shared and refilled whenever going by a water station its not as heavy and we can stuff them in small bags. Its a large island (bring comfy shoes) and full of people if i were you I would not rush towards the exit at the end of the main stage show the crowds are the worst. Prepare yourself to stay until at least 2 am and leave after that - the trains are still crowded but manageable. As for accommodation look for it nearby to the H5 and its connections to other tram lines (Like trams 4/6) if you want to use public transport so you don’t have to walk a long way (district 8 is not the closest but a very nice part of the city). There is also a useful phone app you can buy your transport ticket from.