If it's truly pure LSD, 100ug is plenty. Many hits sold as 100ug really aren't.
That being said, you are more likely to be fine than not on 125ug-175ug, but responses are really variable. I've discovered that I'm very steady on psychedelics and so I can handle physical discomfort (jitteriness etc) and not have a bad time, but there's a certain archetype of individual that has trouble handling the raw barrage of stimulus that tripping represents.
So, you would probably be okay but I would recommend no more than 100ug taken in a natural setting (rather than being stuck inside your house).
(1) Be careful who you choose as a trip sitter. Some people are really bad at it and just end up being super annoying because they're staring at you like you're a zoo animal and keep asking you if you "see colors". Which is a long way of saying, make sure your trip sitter has actually taken psychedelics before, the utility of bringing a sober person along just because they're sober if they don't have psychedelic experience is quite low. (There are some individuals that have never done drugs yet still "get it" so I'm not talking about them to be clear)
(2) Working up doses over time is very good advice, most bad experiences are a result of taking too much in the wrong environment, and/or neglecting the basics. I've found 90% of trip discomfort is solved with water, a blanket, or changing up your physical environment.
But it is worth mentioning that accidentally taking a heavier dose because you think it's a normal dose - can sometimes work out, in the sense that once you've taken, say, 2.5g of shrooms you can't imagine taking 3.5g. I've noticed this particularly with DMT, if you don't get absolutely blasted it's easy to get anchored and be afraid to really commit to a breakthrough experience (as much as I hate the duality / binarity of the whole "breakthrough" concept there's definitely some truth to it)
So: taking a heavy dose as nooby is a terrible idea and thus I never recommend it. But sometimes the terrible idea works out in your favor :)
That being said, you are more likely to be fine than not on 125ug-175ug, but responses are really variable. I've discovered that I'm very steady on psychedelics and so I can handle physical discomfort (jitteriness etc) and not have a bad time, but there's a certain archetype of individual that has trouble handling the raw barrage of stimulus that tripping represents.
So, you would probably be okay but I would recommend no more than 100ug taken in a natural setting (rather than being stuck inside your house).
Cheers.