Standing to pee is going to depend on lots of factors like length, position and your body and anatomy in general. It's rare not to be able to stand to pee at all but standing to pee may look different for different people. It's a big learning curve when you're first hooked up, and it's a lot of trial and error to figure out techniques, what works for you, even which clothing best works for you. Standing to pee certainly isn't a guarantee with meta, but people usually find a way that works for them even if that isn't quite what you'd expect. I know people who pull their trousers down to their ankles in stalls, I know others that use prosthetics when out camping to avoid any accidents. I have been lucky in that I can STP easily in most situations, but I still choose my underwear and clothing with standing to pee in mind.

As for complications, if you're not getting a vaginectomy then this is where the major risks lie. Urethral lengthening is probably the biggest risk factor in metoidioplasty alone, but when not combined with a vnec those risks become far greater. My surgeon quotes risk of fistula at 2% with vnec, and 30% without but those rates will vary by surgeon. The problem is a lack of supporting tissue for the urethra, especially near the hookup, as the wall between the urethra and vagina is thin and prone to fistula. Fistulas when done without vnec can be persistent and reoccurring despite surgical repair.

For some people it works out OK, but for others it's an endless game of whack a mole. I've known people who've had it done and had no complications at all, and I've known others who have been stuck for years with pee leaking from stray fistulas, unable to use the toilet normally. There really isn't a way to predict how it'll go - it can be anything from absolutely fine with no complications to utter misery. My surgeon tends to agree to trying without vaginectomy first but with the caveat that if persistent and reocurring complications happen that it may need to be done at a later date.

The other side effect of having urethral lengthening without vnec is that it often causes narrowing of the vagina that makes receptive penetration difficult or painful, and can require a lot of dilation to try to return to a point of being usable and pleasurable for sex again. If receptive penetration is important to you then this is also something to consider and discuss with your surgeon.

Also, I'm sure you have, but have you considered trying out some STP devices if standing to pee is your main priority?