I asked the same questions of this forum just 3 months ago, I too have offset equipment, 30 years worth, 12 units Goss, 6 unit Heidelberg Speedmaster, 6 unit Harris M-110, and a couple of Hamada's. I too have all related finishing equipment and started out believing that the X box was my answer and I had no need for additional finishing. This forum reminds me what we called "Craftsman Club" in the old days, listen carefully to mail guru and Craig, their answers are right on the money, oh and money, 1/2 mill is the reality if you are going to do it even close to right, IMO.
We started out with a reconditioned KM 6501 and a KM blk and wht machine less than a year ago, when the click bills hit 5 to 7K monthly we decided to go all in.
I personally did not count on offset finishing methods to finish digital short to medium runs, the digital pieces have special requirements that are time consuming on convention booklet makers or finishing equipment, it is tough to cut 24 up business cards with UV on a 36" polar cutter. Someone suggested you identify your needs first, really good idea. We chose short to medium runs as we have the longer run projects covered with our offset equipment. My Heidelberg and duplicators are going to get very lonely. digital printing is not just for medical and religion anymore, it is a legitimate profit center, variable data is a great, almost magical tool, but it requires more than just pushing a button. Read everything you can and then some more because what you think today may completely change tomorrow, identify your budget and the type of products you are interested in marketing.
I notice most of these guys on this forum that really know what they are talking about, don't always recommend specific equipment, but they do suggest what to look for in a machine. I am way too short at this to offer advice, for me the KM 8000 and duplo near line finishing options were my choice. There is a KM tech on this forum who is very helpful, and really not that bias, my budget was 3.5 based on current sales numbers and salaries. To me we got a lot for that amount.
Anyway good luck to you and your business , I don't feel this way everyday but for the most part, I love love love this digital world over the offset I am so used to.
The only good advice or direction I can offer, you are in the right place to get the answers you need, this forum is the best, up until a few months ago I never belonged to one nor had I posted, this post to you is my first ever reply, no advice just my opinions.