I would recommend not getting too ambitious, to start. Tessera has been patching and modding VTMB since it came out and he has learned a lot...but it took him a long time to learn it (not that he was doing it full time or anything but still). It really depends on the skill set you have or can develop. Tessera is mostly a texture modder, though he did learn about various game files and how to edit maps during the years of tinkering with VTMB.
Most of what we've discussed on this forum, in various threads, have been things like fleshing out Chinatown a bit, since it was so rushed by Troika, due to ActiVision's "oversight" of the project (it sat around for six months that could have been used productively, so ActiVision's contracts with Valve and Wal-Mart could be served). But making new quests is not an undertaking for the newbie at Bloodlines modding. Maybe you could try your hand at map editing, to start.
In the Mega-Mod, which is now unavailable to the public, Tessera did extensive map edits, to provide more realistic behaviors to world NPCs, so they would actually move around a bit as opposed to standing in one place. Perhaps you could start looking at doing a bit of that. He also updated the Downtown haven, and added a couple of extra blood dolls to it (with dancing behaviors), though he didn't get around to doing the same for the Tremere and Nossie havens (or Santa Monica).
Schu and I had done some work on writing new Histories for the game (originally separately but we joined our efforts).
Schu eventually finished after I left the project when a combination of technical limitations and my own shortsightedness cost me a bunch of work. I have been flirting with doing a second project along those lines, recently. Schu also
released a mod adding a new Caitiff "Clan" (Oni) to the game. Histories are relatively easy to mod, new clans probably less so.
Does Bloodlines have Italian localization of subtitles and the like? If not, maybe you could start translating those lines into your language. That would help you learn about how those dialog files work in the game with the side benefit of opening the game to an audience who perhaps had avoided the game thus far. That would likely be an ongoing project; as your English improved you would realize better ways to get the meaning across more fully, and update the mod from time to time.
Those are just a few possibilities. Start small and work your way up. This game is NOT modder-friendly like the TES games and such. I don't mean to discourage you, just to instill a sense of realism.