Good morning,
With most weighted movements (Split Squat, Deadlifts) first increase rep count/volume before progressing weight.
The best thing to calculate is 10RM. You want to be working 3-4 RIR (NEVER CLOSE TO FAILURE) for main lifts at a 10RM weight. To keep things simple pick a medium resistance and make it easy with reps (once reps >~12-15 then increase weight and reduce reps). This is your punch the clock/bread and butter working intensity for strength development.
Calculating 10 Rep Maximum (10RM)
Select a weight that you are confident with that is near your 10RM. If you do not know your estimated 10 RM weight start with the bar and perform 10 reps. If you did not fail add 10-20lbs each set until you find your 10RM. If you do not find your 10RM on the first week (4 sets) then continue the progression the following week. Example: Your 10RM weight is 100lbs. You will now perform sets of 7 reps with this weight which is 3 RIR.
For movements like Dead Bug, Bird Dog, McGill Side Bridge: These movements can be as hard as you want them to be and great maintenance for alignment. Once your reps at full extension have reached 8 (with ~3 RIR) increase the hold time for each rep until each rep is 8s. Once you are here maintain and make breathing easier.
Hope that is sensible! Let me know if you have additional questions!