Bicycle Mechanics - Crack on the Downtube!

This, or rather what follows, is my first post of any kind on this or any other forum. So, first time caller and all that?

I had an accident last year in which the down tube of my Bianchi Via Nirone CTC was dented. I saught some advice at the time and as it was on the underside I decided it was safe to use - the stress on the tube going in the opposite direction.
So, maybe 14 or 15 months later I've found a small crack along the line of the dent and I'm now pretty sure the sensible thing is to replace the frame.

The bike is under two years old, but aside from the original Ultegra Groupset, I've upgraded everything else on the bike and want to transfer all components to a new frame? and this is where my conundrums begin;

I don't want to fork out the ?300-400 for a more or less direct replacement - not least becaue I never really thought it was the greatest frame anyway. I've seen Tifosi and Genesis (amongst others, inc second hand) at much more reasonable prices, ?150 - 220, but don't know if the Bianchi forks and seat-post will transfer, or whether they need replacing.

So what snags (they are inevitable) should I be looking out for, what's compatible and what's not? I've seen Sheldon Browns list of seatpost diameters but everything seems older - is it really that complicated for new bikes?

Also, any thoughts on the frame damage? I would have described it as structurally sound before the crack emerged, but clearly this only goes so far. Is there a solution?

It would be difficult to match the fork and seat post to a new bike. There are almost no industry standards for the manufacturers to follow. The fork was also over stressed in your crash if the force was enough to buckle the down tube.
I would try to find a new frame and fork to mount the components on.

You continued to flex the tube across that damaged portion and the crack is Fatigue of the metal.

A Bodge I did when I screwed up and did similar front end damage , involved cutting a section of same diameter tube slitting it open and brazing a patch, sleeved over the damaged portion.

You can stretch the front center out , back to nearly its original dimensions in the process. it has moved back a degree or so, I expect.

requires metal working tools, a modicum of experience, and Shop Space, to do the above .
or hiring the services of someone that has..

frame replacement is perhaps more straightforward

many people like the Surly and Salsa Brand stuff that are QBP owned brands , sold thru most dealers.

I'm pretty sure that model of Bianchi has aluminum main tubes, so you can disregard the previous poster's advice.
Just replace the frame with one you'd like, and buy a front derailleur and seatpost if your old ones won't work. You can always sell your old ones on eBay or such to supplement the purchase.

Wheelset, crankset and brifters are the more expensive components and will transfer over to pretty much anything as will your RD, stem, bars, saddle, pedals, etc. If the seat post and FD fit, great. If not, they are not going to be big hits if you need to purchase.

thanks for the replies folks