one of the better tools to that end is http://kobold.club/fight you get to decide the total session pool, how much you want to expend of the party resources with this encounter, and how much xp to award at the end. In dnd it is necessary or you'll get a TPK which is for some reason bad.Wow. Not coming from a D&D background, I'm a bit amazed a DM rely on some kind of pre generated weighting system of the developer to determine encounter.
you mentioned about the weakness of MU vs Paladin. Well in 5e thats not the case any longer. A MU has more HP than OSR, they have continuously available magic (Cantrips) that can cause some fairly significant damage, some of the classes have have abilities that allow a recharge of spell slots with a short rest, and Magic Missile auto hits and does between 6-15 damage each time it is cast. Conversely Paladins powers always take a long rest to recover, weapons do less damage than in prior editions and monsters generally have slightly higher ACs so they are very much on par, especially at 1st level. and lets not talk about how much they nerfed higher level magic users...