Didn't had an evil pc here but in long-forgotten TT campaign, so will give of more general answer
In order to play an evil character you should really think through about alignment and what caused it. Having a solid ground for a character to ignore someone's suffering, being ready to commit crime or worship devil (just examples) will made the experience of playing one enjoyable for you at the first place. Just "My character would do that" is considered a poor excuse, as far as I know, so giving him some childhood trauma/ cultural aspects to justify behavior and actions is a go to (but that is appliable to all characters, if being honest). Also, keep in mind that alignment can shift but do not do so easily and especially cannot do so on a whim without using enchantment magic.
If you needed some guidance on which alignemnt to pick, I would recommend Lawful/Neutral Evil. Chaotic Evil usually doesn't hide itself, which means that you will quickly get in conflict with Good-aligned characters (which is ~60% of active basr at the moment?), which may result in pvp and you will likely be stuck with Soubar and other evil-themed locations. Neutral and especially Lawful Evil creatures usually make efforts to not reveal themselves as one until the point where they can do so safely for them.
Spoler: Evil always acts for his own profit even if it means using others as expendable resource and won't do anything that could harm them. So, they need a decent self-preservation instinct and planning
. So, you can try playing a covert evil and reveal yourself when noone can stop you, play it open and likely face some hostility from good-aligned chars (but that would depend on what you do infront of them, actually), play it open and join other evil characters or come up with something else. Evil characters
can work with good ones in team by the end of the day, if they have a common goal and not actively trying to screw each other. Not a common thing, but it does happen
As for the questions of forum, metagaming and such: if you do something, there are chances that rumors will spread - but not guarantees. And using information from journals and public bio's are usually frowned upon, unless I misread rules.
On other side: if someone tries to find information about your character on forum or just stumbles on rumor and read it - doesn't it mean that you made an interesting character?

So, can't say that my sheet of text will help much. In practice, as one of DMs said : "Let it flow", roll up a character you like and want to play, give it a few shots, see if you actually like playing him and try to find few people with who you can play him without being concernced. And just have fun in the end