Start a new character when it feels like u can't progress with your current one. It makes you realize how much better at the game you've gotten, is a good training and helps you find everything you might have missed in previous playtrough.
Also very few bosses are actually mandatory. The first boss is optional.
Learn bosses weaknesses and abuse them. Wether it's elemental weaknesses, AI glitches or limited moveset; they can make farming unnecessary.
Don't forget chalice dungeons, they give nice loots which will help you run trough the main game.

Unless you want to take a huge, huge detour which will have you fighting against another optional boss, then yeah, I guess you can consider the first boss optional.

Hopefully you have a ton of patience. I do not, personally.

practice makes perfect. Most Souls player dive hundreds of hours into these games. Once you have this foundation, the games becomes very satisfying, both pve and pvp.

You can just get to father gascoigne once you've opened the last central yharnam shortcut (central lamp -> house) and get going towards the tomb of oedon just like you would have right after beating the cleric beast. Father Gascoigne is not optional as he gives the tomb of oedon's key to get to amelia, while the cleric beast only gives you the hammer.

The gates that take you to the Cathedral where Amelia lies are closed unless you defeat the Cleric Beast, which will grant you the Hunter handkerchief, allowing you to bypass the gates. It's either that or taking the huge detour by going to Old Yarham.

He's on about Old Yarnam and BSB.

Also don't listen to the noobs about the threaded cane, skill based weapons are the best in the game by far as many enemies are weak to stun lock, and if you get good with the threaded cane most bosses in the game become a comelete joke. 

Also make sure, for bits you start finding difficult, use the fire and bolt paper buffs, fire is especially useful early game.

Also to level up if you find yourself in a sewers area find the tall lader that off of a woden platform, as at the top, in the midsts of 5/6 crows, is an item called Mad Mans Knowladge, which if used gives insight, which activates the NPC in the hunters dream that facilitates leveling up.

Practice parrying on the exocutioner (the guy with the big ax on his tod) as parrying can trivialize many parts of the game, including bosses.

Don't bother upgrading Bloodtinge, it's a pain in the arse to make a good bloodtinge build, and parrying is what's really important. Also don't bother with Arcane past 15, as 15 allows access to the Old hunters bone, which is a massive help in dodging harder bosses, other than that Arcane builds require excessive chalice dungeoning to get the right set of gems, and the chalices suck until you get RFC depth 5 root dungeons.

Also, git gud.

EDIT: also, counter intuatively, dodging towards and either slightly left or right is often the best way to avoid attacks, and gives the best oportunities to attack.

I don't do hard mode at all and was worried about playing this game (my greatest fear is starting a game and not being able to complete it due to difficulty). I died a lot on some bosses, but in the end I managed to do it. 

If you've played the real Devil May Cry games on normal or above you should be fine. 

I think it helped me when I grinded the first area. I used the area as a practice zone to learn patience and strategy. 

Yup, totally wrecked some bosses by going psycho and attacking like there was no tomorrow. Works better when you co-op as one distracts whilst the other delivers the pain. 

https://youtu.be/kJgZsXOVuH4

If you do get stuck, you can always bring in people to your world that could help you with bosses. 

Have they fixed the time it takes to reoad the game after you die?? That's what made me but this game down... that horrible long load time each time you died..