Is Klingon gameplay still PvP oriented or a Klingon characters can be played also with a good amount of PvE? As a roleplayer I will prefer Klingon to Feds, but generally I haven't so much time to play "seriously" in PvP.
Don't worry, in the current state of the game you won't even get much of a chance to PvP on the lower levels and you also won't need it.
There would not be enough missions for a Klingon char, if it started as it did at level 6, to get to max level without excessive grinding along the way.
So the "solution" Cryptic added for the Klingons were no new missions (which would have been preferable) but instead, as you mentioned, they increased the starting level to around 25.
This does not only apply to the requirement to create a Klingon char but also to the starting level of the new char.
[Should you wish to read a bit more about the reasons for this and why so many Klingon players and whole fleets left this game months and sometimes even over a year ago I'd like to recommend
"The History Of The Klingon Empire With Cryptic Studios" written by the player known as "Peregrine Falcon" here:
you will note that everything he writes can be backed up by quotes and articles.
It should also shed some light on the reasons why, around the KDF forums, you will sometimes note a less than enthousiastic attitude from posters towards Cryptic and their choices regarding the Klingons.]
With the current amount of PvE missions it is supposedly very well possible to get to max level using those missions alone without any PvP.
I made a new Klingon char after Season 5 to try that out myself but haven't had time to get very far.
But I know there is a thread where someone mentioned he managed to get a post-Season 5 KDF char to max level in about 8-9 hours.
However that was during an event where you get twice the normal XP.
And he probably knew the missions by heart.
So you can of course double, triple or perhaps even quadruple that amount when you factor in the need to get familiar with every mission, properly enjoy it, and get decent gear along the way.
PvP is nearly impossible aside from max-level since there are currently so few opponents queing up for Klingon vs Klingon or Federation vs Klingon fights.
So it's basically the same amount of options at max-level as with the Feds.
Meaning PvP, Special Task Forces (5 people "raids") and of course the Daily missions.
Thanks to a recent change in the STF mechanic it's possible to fight alongside Feds in STFs, which adds a bit more diversity.
Unfortunately beyond that this game lacks any impressive endgame content for both sides equally.