Soma is rare until haru appear, which is around august period, u can ask her to plant SP recovery for u, just collect from her every 3 days.
1st palace is the hardest to go through, but u just need to spare a good 5 days trip just for the palace, it shud be relatively easy, every safe room u reach, just exit n recover, come back the next day.
and there is one confidant which is very important to max it, which is the teacher/maid, miss kiwakawa if i nv spell wrong, max her fast when u get the chance, once u max her social link, after every trip u come back from memotos or palace, usually morgana will force u to rest, but with the teacher max social link, u can call her to ur room for massage, this will give u the chance to go out again and progress some other social link like chihaya and ohya in shinjuku, maxing chihaya has alot of benefit oso, her fortune telling can enhance ur loot n money dropping from battle, and when u max her social link, she can up ur affinity fast, means those social link that needs u to go on empty trip to gain more affnity before u can continue their story, u can spend 5000 yen on chihaya to ask her to up those affinity and straight away continue the social link without wasting extra days.
final palace in prison, every battle will give 3k-10k of exp from trash mob, and 30k-50k of money dropping from every battle.
i go in to the palace at level 63, after the palace (which is not very long), i was already lvl 78. with 2 million yen.