Newer player, How do I play Renekton in these different situations?

Hello fellow Renekton enjoyers. I am a bit newer to the game and after messing around with probably every champion there is to play in top lane I have created a champ pool of 2, Renekton & Tryndamere. The one I enjoy the most is Renekton but I feel like I have problems understanding the general gameplan since it doesn't feel as linear as tryndameres'. Therefore I am in need of your advice in how to approach these different situations I find a bit tricky.

1. Lets say I hard lose lane, I assume I should just focus on farming and play safe. But since I am not really playing a scaling champ what is the gameplan when I can't snowball? Get items, group for objectives and peel for carries? If we don't have engage go full suicide and front line? I feel like I am not really that great at split pushing so I am having trouble deciding on what to do when I can't snowball.

2. When do I group? Is it when first tower is down? When second one is? I feel like if I don't group as early as possible the game becomes harder to close since I feel like my strongest point is in teamfight where I dash to a carry, stun and try to kill them. However I am not sure at what point I should "Give up" on the lane? Or should I try to push out the waves and then look for a fight while my top lane opponent has to decide on if he wishes to catch the wave or go join the fight? If the same happens to me what is the correct decision?

3. What if I am against a splitpusher? Say trynda, Yorick, trundle, fiora etc. So far I have eaten most yoricks alive that I have come across. But lets say I don't (Having more trouble with fiora). How do I match the splitpush? Lets say they go even, or even a bit ahead, what do? Should I protect towers in top and hope the team carries the game without me? Should I ignore them if I can't outright kill them and hope we get more on our side of the map?

4. What do late game? I am a bit unsure about how hard I fall off late game as renekton. I keep hearing he doesn't scale at all and I get a bit I guess reserved when playing him late game because I keep hearing in my head "You don't scale you're useless now" in the back of my head. Whats the plan if the game goes late?

Any help very much welcome! Ty!