Help With ranked- Top Lane

I was Gold 5 last season looking to climb back to Gold this year then stop playing ranked. I got placed in SIlver 3 and so far I have won a game to put me at 26 LP then lost 2 games to put me back at 0 LP. This post is basically if any top lane main could help me out figure out the problems I am having so far that I have noticed.

My Farm- I usually play tanks in top lane but when I can I will play fighters or carrys that being said if you look at my match history my farm is absolutely horrible I have noticed this because I usually only get to farm during laning phase then when the team wants to group they always need to tank there to engage and keep them safe, what can I do after laning phase to keep my farm high? usually when I go to a lane the enemies just start pushing and the team needs me.

Teamfights- Another problem I am noticing is during team fights I am not sure who to focus, A couple games ago I played nautilus and I always ulted the enemy adc and killed her during the fight I then turn around to notice all the carrys on my team are getting slaughtered by the enemy team and I don't have enough damage to stop them. In teamfights if I am the only tank on my team should I be peeling the adc or do what I did which was going for the enemy adc?

Roaming- When I get ahead in lane I like to roam mid or teleport bot trying to get a kill or dragon but when I roam though the enemy laner usually gets caught back up in cs and I have to stay top again to make sure he can't get a lead. I know decision making is usually the key to roaming when and when not too but is there any advise out there from when it is the best time to roam during laning?

If any one can help me out with my questions that would be great, thanks!