For such long thick boards I would say a spring joint is essential. The main reason for springing boards is that the ends try out faster than the middle of the board and can cause the joint wood to break open on the ends. The springing adds some compensation for this and assuming they are fairly close to final moisture levels prevents the cracks appearing.
The Sedgwick P/T is ideal for jointing this kind of stuff two rollers or a helper and you will achieve excellent results. Sometimes to help extending vertically the fence gives more confidence your not 'wobbling' piece of 18mm mdf with toggles / buttons on the end to clip to the fence is all that's required.
Any plane you have can be used to spring the joint.
I would have a go with one board.
To remove the tear out if you want to stick with what you have I'd try card scrapers. No risk of tear out of the top surface and a far better finish than sanding. My solution would be however to rejoint on the sedgwick
The Sedgwick P/T is ideal for jointing this kind of stuff two rollers or a helper and you will achieve excellent results. Sometimes to help extending vertically the fence gives more confidence your not 'wobbling' piece of 18mm mdf with toggles / buttons on the end to clip to the fence is all that's required.
Any plane you have can be used to spring the joint.
I would have a go with one board.
To remove the tear out if you want to stick with what you have I'd try card scrapers. No risk of tear out of the top surface and a far better finish than sanding. My solution would be however to rejoint on the sedgwick