2-3-4, depends on the rod. hahah
I have lots of rods and try to keep them limited to one or two lines but there are a couple rods I have more or want more lines for. Spey rods are easier as you may only want one or two lines, say a Skagit and scandi where a switch rod can throw any type of line.
My spey rods are set up with Skagit lines with another set of reels with windcutter lines for them. I have a couple of scandi lines for a couple of them.
I am also not a fan of extra spools. I would rather just have another matching reel (then you can switch spools too if you don't want to remove the reel.
If you are switching lines fairly often buy heads and a running line. They are quicker and easier to change out a head over a whole line. less tangles to worry about too. I have a bunch of outbound lines and I am thinking of cutting and looping the ends for just this reason. It is a pain to switch out a whole line and I don't want to buy a reel for each line.
If you find yourself getting a lot of lines Roi's head case helps organization a bunch. I picked one up for my SH lines last week and just got another for my spey lines today.
I have one switch rod 5wt I keep with a switch line on it for indicator fishing for trout. My other 5wt switch has a Skagit line on it. I fish from a raft a lot so I can leave my rods out and pick up the one I want at that moment.
It sounds like you need 2 reels or a reel and a spool for each rod if you are going to fish 4 lines on 1 rod. I would get one set up with a running line then you can switch between Skagit, scandi, or overhead (outbound heads). The other you can put the switch/indicator line on and fish in the spring.
Warning: If you get another rod you will just end up wanting 2 reels and 4 line for it
Ask me I know.
I wish I could do more fly fishing in the ocean, stripers sounds fun. Good luck.