Deliding is not a NEED it is a WANT for people. It can lower your temps by a good margin and is a step highly recommended if you want to try and push your overclocks as far as they can go. If you are only aiming for 5.0 GHz chances are your temps will be fine as they are with the Noctua NH D15s as that is a monster cooler. Delidding does void your warranty but many delid kits trivialize it and make it less dangerous to do. I would recommend not deliding if it makes you nervous as it can run just fine as it is.

If you intend to run stock speeds or play with mild overclocks, delidding a CPU is unnecessary. Folks that fall in the delid category are going to be pushing past 5GHz overclocks or are going to be running their CPU 24/7 at near 100%. For you, delidding is an unnecessary evil, not recommended.

You cooler is fine, actually it is a very good Air Cooler. Whomever advised you probably is in the camp "liquid cool or bust". I will tell you a little something - 90% of all those All in One Liquid coolers are actually worse at keeping a CPU cool than a good quality fan cooler. Subjective, depends on cooler of course. I have owned three All in One Liquid coolers and all three were, at best, fair. DIY liquid cooling is where it is at, but it will add $400 to your build, bare minimum. An Air cooler is mostly the wise choice outside of serious overclockers, those whose PC's cannot accommodate anything other than a low profile air cooler, or those that want to get their builds featured (aesthetics of a custom loop).