New to the site and I appreciate everyone’s feedback in advance🙏.  

My idea is using a 6/3 romex from the main breaker box in the basement to a junction box, spliced it and connect it to 4/6awg copper THWN including ground into a 1” or 1 1 1/4” sch40 pvc conduit to the garage. 

Questions:
1- Will a 60amp breaker be enough for my garage or do i need to up to 100amp, will change the whole plan? 

2- Can a junction box (as shown in the picture) be use inside the basement or it has to be outside?

3- Does pvc conduit needs to go straight to the underground or can it transition from cement into underground? I know it has to be buried 18”.

4- Should i use a main lug or a main breaker box in the garage? 
[![junction box][1]][1]
[Garage][2]
[![][3]][3][![6/3][4]][4][![house joist][5]][5]


  [1]: https://i.sstatic.net/oLGOh.jpg
  [2]: https://i.sstatic.net/dcDT5.jpg
  [3]: https://i.sstatic.net/2JcsX.jpg
  [4]: https://i.sstatic.net/8CYI9.jpg
  [5]: https://i.sstatic.net/rWL2w.jpg