The reliable way to hire a tradesperson

Super amateur painter, I’m creating panelling in my room by using a 9mm sheet of mdf and routing grooves in them to create a ship lap effect and sticking this to the wall. Will I need to seal/ prime the mdf and what paint will be best as the top coat for this? It needs to be quite durable as it’s for a kids play room TIA

I've had a log burner fitted before the summer so had to break through an old fireplace. When finished the wall above and around the fireplace was plastered. It now needs wallpapering, which product do I use for sealing the plaster before wallpapering

If a patio door is difficult to close as hitting the rim can it be realigned ?