I'm currently replacing floorboards in a room that measures about 7m wide. I think they've been replaced before is they don't exactly line up with adjoining boards and where there do join they seem to be cut at an angle. There was also a big patch job of chipboard. The existing board/planks are t&g but I'm replacing with planes all round planks 18mm thick and packing on each joist to raise the level. Screwed into each joist which are at roughly 10" centres. I've also noticed that there's a slight fall from the cut line which joins into another room which was an 80s extension (therefore I can't make this area level as it would leave a little step). The house is Victorian. I plan is to then lay 6mm ply, 3mm insulation and engineered board. Do people think this slight fall will later cause a creaking issue or will the engineered boards settle to it, I'm fine with the slight slope. I also need to reduce height in a small section of it, I just plan to use an electric planer. Good idea?