Davies is the more important immediate signing, he's been playing in this country and can more quickly be inserted into the team in lesser games, allowing Fabinho or Henderson to rest or play in midfield (so our midfielders can rest). We can't expect Thiago or Wijnaldum to play 90 minutes every match, and we're still using Milner a lot who is 35 and also is a cover for our full-backs. I don't think Davies is gonna play a lot in CL or against top half teams. Kabak as a loan with option to buy makes sense, he's 20 and if we can get him adapted to our style by end of season he can be a bargain, otherwise he can be let go while still offering some cover at the back this year.
With Gomez and Matip as injury prone as they are and uncertainty around VVD (player fitness can change after ACL injuries), we still need to sign a big world-class centre back in the summer.