With the way solo queue works now, you don't NEED a mid laner. You can focus two lanes, and have some back up supports in case you get auto filled. You say you are an adc main, so obviously thats a role you would focus. You listed three jungle champions, so I'm guessing thats your next most played? You could main adc and jungle, with a few go to supports for when you get auto filled. Or, if you prefer, you could main adc and mid if you prefer. Just stick with two roles instead of spreading yourself too thin.
In terms of being an adc, or any carry for that matter, its useful to have some go to picks to change how much utlity or damage you bring to the table. For example, if you get the adc role and see that top lane is a riven and mid is a vladimir, your team's cc likely all comes from your support. In a situation like this, an easy champion like ashe would be preferred as she can sometimes peel for herself as the other lanes certainly won't do it for you. On the other end of the spectrum, there are pure damage adcs like jhin who can't protect themselves very well at all but work wonders on teams with two or more high cc champions to defend you.
Picking a champion who is currently good can be fine, but it is generally better to main reliable champions who don't occasionally become "too good' or "utter trash" based on the latest item updates or meta shift. For example, don't main ezreal as he has a tendancy to flip flop between godly murder machine and "meh".
As for easy supports, I would stick with tanky cc champions as they provide much more to a losing team than many mage supports do, and most other players will pick there favorite damage champs anyway. There's braum for when you have high attack speed low mobility adcs who can proc the stun easily and need a body guard. He's easy to play and after a few games you start to get when to be a guard and when to lay the smack down. Nautilus has CC on every ability AND his auto attacks. He is also VERY hard to kill and has both engage and disengage. Nautilus also is very easy to play, with the biggest learning curve being understanding how tanky you are, and when you can all in. If you need a damage support, go Zyra. Thanks to how she deals damage, she only needs a liandry's torment and a rylai's crystal sceptar to be useful for the entire game and deal relevant damage and cc at all stages of the game. It may be worth having a healing support like soraka, but their viability is rather shakey from patch to patch.
