Those are quite a lot of questions but I'll try to answer them.
1. Is building sightstone a norm for competitive/ranked team based games?
Having two Sightstones in a team is really beneficial in a teamgame with communication. Vision is always important but in higher ranked 5v5 games or even LCS it can decide the game. Also in higher-ranked 5v5's you'll find a lot of junglers going full-tank and playing for the lategame where the sightstone doesn't hurt.
2. Can I build it on a soloqueue jungler? 3. If yes, when?
This one's a bit tricky. Soloqueue is usually a lot about snowballing and getting the most out of aggressive items. Champions like Lee-Sin or Jax greatly benefit from the item because it offers them a free defensive gaplcoser, however on a lot of champions you shouldn't get it all the time. It's still very safe to pick up on most champions if you aren't extremely fed. The vision will also help you in soloqueue but it's not as impactful as in 5v5's. If you're really ahead on a soloqueue jungler you should usually go for either damage or extreme tankiness to end games quickly.
4. On which champions can I buy it?
You can definitely build it on champions with a targetable gapcloser (Lee, Jax) but it works on really pretty much every champion that builds somewhat tanky. Evelynn, Rek'Sai and even champions like Xin'Zhao can build it to help their team. Just always keep in mind that Sightstone isn't a very good Item in direct fights.
5. Would those champions have to purchase Cindehulk for the Sightstone to be more effective on the health stats?
No this isn't necessary. You can potentially go for the warrior enchantment and rush Sightstone afterwards. Just keep in mind that Cinderhulk is still a very strong Item after the nerfs and makes the item more effective in general. So if you're playing a Jungler that naturally builds Cinderhulk a Sightstone doesn't hurt.
6. Where would I ward on Red/Blue side for the laning, team objectives, mid and late game?
You will usually have your sightstone midgame. If you already have it during early game you're definitely buying it wrong. Usually your supporter should have his Sightstone about 5-10 minutes before you get it. This basically means that it's his job to ward the bottom side of the map (you can still help obviously) but you should focus on warding other areas. Depending on the flow of the game you can try to go for aggressive or defensive jungle wards.
7. Considering I purchased sightstone where would I sweep for wards when behind or ahead (red and blue side)?
First of all: You should almost always get the sweeper as jungler around level 9, regardless of whether you have Sightstone or not. Now sweeping is somewhat tricky. As soon as you upgrade to lens the cooldown is very low and you can sweep pretty much every time you feel like there could be a ward around. The only times you really have to keep your sweeper is if you want to camp somewhere or you want to do objectives. Depending on the enemies you can also wait for the teamfight if they have a stealth champion that would be revealed by the lens.
8. Where would I plant my pinks for both sides of the map when behind or ahead?
As a jungler (or player in general) it's really advantageous to carry an extra pink ward with you. In case of your team wanting to do dragon you can simply put it into the pit and clear everything. Apart from that The Death-Bushes, Tri-Bushes and the Bushes behind the redbuff are always a safe spot to put a pink ward in. Depending on whether you're behind or ahead you can simply put them in the respective team side.
