I have a 2000 Land Rover Disco 2. I bought it in 2014. I am not good at working on cars. Questions near the bottom, just wanted to explain a little about what all happened.

The long story is about 2 months ago I went out side on a warm day (90's) and noticed a puddle under my rover. I checked and it was antifreeze. Started doing some looking around and found that my expansion tank somehow broke and was leaking. Ordered a new one and seemed good. About 3 weeks later walked outside on a warm day (mid 80's) and there is a puddle under my Rover. Searched and searched and could not figure out where it was leaking. About 3 ago I took it to a local shop and they told me it was a few hoses lose and some bolts. They tightened everything up and said it was good to go. They had it for 2 1/2 days to clean the engine and search for the leak. Day after i got it home the puddle was back and twice as big. Waited the weekend and took it back to the shop. Now its the water pump. Now ill mention here that the week before they said it might be the pump but then told me it wasn't and was the hoses. So get a new water pump installed. They had it 2 days i think. When i go to pick up my rover, it takes them 5 tries to get it to start. No previous starting issues. They keep it that night and tell me the next day it needs a new starter. Took it in Monday for the water leak got it back late Thursday after the starter was installed. On my way home I glance down and notice my speedometer isn't working. I call Friday and tell them the speedometer is not working and they tell me to bring it back Wednesday. I drove it 4 or 5 times from Friday to Monday. Once a few hours after I first noticed it was not working on Thursday it briefly worked but then stopped again and did not work again. Dropped it off Wednesday morning and finally got it back Thursday after 330. I was told that some wires under the drivers seat and passenger seat were loose / not grounded and that was causing the issue.

Also with the speedometer not working there were 4 new lights on the dash on that had not been on before. first three are yellow brake light was red.
Hill decent light
SLS Warning light (I think. it looks different on my rover from all the pics I can find online)
ACE warning light
Brake light

So my questions are,
Can installing a new starter (unhooking and rehooking the battery) cause a short or anything to do with the speedometer?
Are there any wires under the seats that have to do with the speedometer? Ignore this question now that i have learned of the ECM
Edit: So I was told that some wires were loose that had to do with the ECM and TCU. can replacing the starter have cause an issue with the ECM so that the speedometer would have stopped working? If the wires were loose on the ECM and TCU wouldn't the speedometer have already been experiencing issues?

Not knowing what all they did or messed with I'm at a loss as to what they could have done to cause the lights to come on and the speedometer to stop working. Having never had an issue with them before. Since I have had it the ABS light TC light and check engine have been on. but never had an issue with any other lights unless I turned really sharp and 1 out of 10 hard turns and the ACE warning light might come on and ding at me until I turn the rover off and back on.