This is a tricky one. There's no right answer and there's as many answers as there are people. In my version of "reality" I would avoid dating while trans but I can't help it.
(Little background, I'm 34, full time for almost 3 years(ish?) hrt for around 4? I'm not sure, I think I started right around the time I turned 29... After YEARS of being run around by the health system here)
I think dating depends on a few factors (please nobody attack me for any of my opinions, that's all they are, my interpretations of my experience viewed from my perspective, that's all. I'm aware of my "privilege" being white, middle class, educated blah blah, anyway.....
Do people assume you're cis, In person in broad daylight? Be honest with yourself. There are a few things that I noticed happened when I discovered I "passed"... Men will approach you when you're out, Ask for your number, want to dance with you, make conversation, try to kiss you, ask if they can see you again etc.
This is always very awkward for me because my policy is always a straight up "No"
Too much risk involved.
Keep in mind, most men don't murder trans women, but most trans women that are murdered, are murdered by men...
One thing I've always struggled with is, how to be intimate as a pre-operative transsexual woman. Sure there's things you can do but, depending on your particular feelings about your anatomy, intimacy is incredibly difficult, frustrating, triggering and often painful. Do you have a plan to cope with this when you're thinking of dating this person?
Are you hoping they "won't notice" while you're being intimate?
(Fun fact, I tried this once to test if I "truly passed" he "discovered" about 30 mins into us becoming intimate... Wasn't impressed but, wasn't the end of the world but, it did bring all festivities to an abrupt and early close... I was lucky (and drunk). I'd never do that again and I certainly wouldn't recommend it, I was f**cking terrified. He never spoke to me again)
This brings us to online dating...
I honestly believe, if you're pre-op, this is your safest, easiest option. You can put pictures of yourself, they contact you, you chat for a while as human beings. Then maybe you meet for coffee (during the day, in public...derp)
I'd recommend NOT letting them know prior to meeting in person. So you're first and formost, thought of as a person, not a medical condition with a scary, culturally loaded, name like "transsexualism"
After you've met, provided there was a "spark", let them know online, while you're safely away from them. Don't give them your phone number, tell them where you live or work before you both know each other a bit and are satisfied you're not going to be hurt/outed/etc (these are basic online safety rules for ANYONE online dating though.. Not just us)
I met my current partner this way. It's very early days (5 months) but, we get on. Things are good, he's ok and not a creepy fanboy ->-bleeped-<-, or a cross dresser trying to live vicariously through me. Dating while preop isn't great, it's complicated. Sex while preop isn't great, it's complicated. But, we're often viewed as complicated people by comparison so, depending on your local cultural norms, it will be this way for a while.
If you don't pass as cis (visually, physically, vocally etc) I don't really know what the options are because I never put myself in that situation but, I'd always go the online way, for safety.
Same as post-op.