Assume your budget is low based on your current gear. My Dad called crappies Paper Mouths for a reason. Just my opinion, but I would stick with a spinning rod for crappies.. That way you won't need to worry about getting a rod that will load with crappie size lures, and a reel that will throw those weights. Plus light lures on a baitcast reel are not for beginners. They also require some specific gear which normally costs quite a bit. Plus a rod suitable for crappies will be a little on the light side (power wise) for the other species.
The good news is any reel should handle pretty much any lure you would be throwing for the other 3 species.
Telling us you fish for crappies, bass, walleyes and northerns isn't a lot of help. Preferred lures (and weights), techniques and cover type would help a lot towards getting good suggestions. A good all-around rod will be either a MF or MHF ranging from 6'6" to 7'3" length. A reel with a ratio in the 6s is considered a good all-around ratio. I am starting to like the faster ratios as I have no problem slowing down, but often don't reel fast enough when the situation calls for it.
What reels did you find? Post what you are looking at and I am sure someone will have an opinion about your choice. Might not be the right opinion for you, but hey..............
EDIT: Everyone backlashes on occasion. Probably the best reel to start on would have dual brakes which work on both ends of the cast, or a centrifugal brake system which works on the beginning of the cast where most backlashes occur. I learned on a magnetic only. It would be my last choice of those 3 brake systems (unless it were my Zillion 50th). However, for a backlash free reel, find a Daiwa with Magforce 3D braking. Unfortunately I have a feeling it would cost more than you are willing to spend. Approximately $200. Another option might be a round reel. I have some Ambassadeur Black Max 1600C reels that are pretty hard to backlash. They are plenty small enough to palm. Naturally the used market is the only place to find one. I would assume the larger sizes (3600 to 4600) would handle similarly and would make a better all-around reel.