Romance help for new trilogy run

I didn't really have to deal with this since I'm straight and female, buuut... I hope I can still give you a little input.
You could certainly play a bi man if you want. I would recommend to romance Ashley and then break up with her in ME3, because you will get a pretty good scene with her doing that (in my opinion anyway).
Alternatively, you could also romance Ashley, let her die, romance someone in ME2 (Samara isn't really an option until ME3 and then only in the Citadel DLC, but you can flirt with her in ME2), or just sleep with Jack. She will hate you for it, but I did that before as well and it was interesting to see. You could of course also flirt with Kelly enough to get her scene. I plan on doing that in one run where my Shepard will end up with Steve.
It could also be interesting to romance Ash in ME1, let her die, do Kelly or Jack in ME2 and then get together with Kaidan in ME3. Could be a nice build-up because he and Shepard had to go through all this together, they have a history that Shepard doesn't really have with other characters.
I have not done Tali's romance before and don't know how it is, it's going to be my next romance though.

Liara seems a little needy for my tastes so I've never been that interested in romancing her.  Don't care enough for Ash to romance her.  If I feel the need for a romance in ME1, I do the gender swap thing in ME1 and deal with quirks (being referred to as "ma'am" and "princess").  Otherwise, I'd rather wait.  I think Kaidan is worth it.

EDIT: I flirted with Kelly in ME2, we had dinner, but never invited her back for the lap dance.

None that I've seen.  I've always been told to create a FemShep with default features and then use a console command to change her gender.  ME2 and ME3 have had more ability to use mods to make changes than ME1.  Probably because console commands were so wide reaching in ME1 that mods were often found to be unnecessary.

LOL I love your idea about romancing Ash then leaving her on Virmire!! As far as ME2 goes - I'd romance someone secondary cause I'd miss them in ME3 if they die on the suicide mission.

If I romance ash and she dies, does Shep keep mentioning it in ME2/ME3 or is it mainly contained to ME1?

I think it's bullshit there weren't any gay-male romances until 3, but I also think some of the other romances can be fun. I haven't done ALL of them yet myself, but:

I personally really like Steve's romance and think it's worth it, so I would recommend it since you've never played it. It's really not weird or creepy or depressing like it might seem.  He's not a squadmate like Kaidan but he is your shuttle pilot so it didn't feel lesser to me because there's still other content to experience (especially with Leviathan and Citadel dlc) -- just make sure to talk to him after missions if you don't already.

I've done the romance-Ashley-then-let-her-die-on-Virmire which makes for an interesting story, although entirely in your head because, as stated, the game itself doesn't reflect it... Or you could always start with Liara and then say maybe her and Shep just grew apart during 2?

Going into 2... Perhaps Jack? I, again personally, like her ME2 romance and she's pretty chill about breaking it off in 3, so it can feel like maybe the relationship either didn't work or just ran its course, or whatever else the case might be for your Shep. For Tali, it's super sweet and nostalgic but I feel that her romance only gets better in 3. And Miranda... well:

I've never done Kelly, but she could be pursued without feeling too romancy or serious, I suppose?

Anyway, imo it's worth trying out new romances to see how they'll fit or to do something different, so have fun with it.