I heard that people have 5-20 keywords per adgroup but I have many that have 50-100 keywords and they are all very relative to that ad and adgroup,
could that still be a problem ?

When i was doing adwords i only had at most 1 keywords per adgroup. This allowed me to write specific ads for adgroup. 4 or 5 similar ads for 1 keyword, yes it's more work but the roi is better.

Yeah ..it would be best to target long tail keywords only because the conversion is higher .
If you enter too much keywords and i believe most of it is repeated which is waste of money .

No, it's not bad to have 75 keywords in a group. You may do better however to carefully look at them and split off into other themes.

For example, I had a client selling kitchen countertop. He had one group with many keywords such as "wood kitchen countertops" and "granite kitchen countertops" and many others adding geo-keywords such as "granite kitchen countertops mytown". The better thing to do would be to put all the "wood" keywords in one group and the "granite" keywords in another. Better still, the "wood mytown" keywords in yet another group. You could still have a dozen or two keywords (all match types) but it should make it easier to manage and create more specific ads based on what people search for. This will improve your campaign and ROI.

Its not bad if those kws are extremely related, because don't forget, all those kws will trigger your ads, so if theyr not extremely related then your ads wont perform well. If I were you, I would filter out as many Kws as possible and create different ad groups

I have ad groups with 110 keywords, with most having 10 quality scores.
It works for me as all of these are virtually the same, with slight variations in spelling.

This may be overkill, but by no means am I penalized for this setup.

Most ppc experts will tell you to limit yourself to 3-10 keywords per ad group...simply because the odds are you will be using keywords that have a slightly different theme.... which will hurt your relevence, which will lower your quality scores, which will lead to you paying more per click.