Basic Strength Training for Triathlons

I have never been disciplined about strength training. Every time I have tried it, I'd do it for a few week and as my endurance training would go up, I'd gradually stop strength training. Instead I should scale back on strength training. I am currently start on it slowly and hoping to add more routines gradually. My current routine is only upper body and core since I just ran a marathon last weekend and I am still recovering. I hope to gradually start adding leg strength work into the mix.

Upper Body & Core:

• Biceps + shoulder press (10 reps)
• Biceps + shoulder press + push up (10 reps)
• 2x:
• Biceps only 10 reps
• Shoulder Press only 10 reps
• 2x: 
• Triceps (10 reps Left, 10 reps Right)
• One hand row (10 reps Left, 10 reps Right)
• 10 min core (follow a YouTube video)

I will gradually add these exercises to the routine:

• Leg strength for running/cycling
• Split squat (gradually increase difficulty by adding weight)
• Arabesque (helps with glutes/hammy activation and control)
• Hip glute bridge (both legs and then single-leg to add difficulty)
• Calf raises OR jump rope 3x 30sec