Looks like you have some common problems. Lets start at the top.
Tachometer: May be one of 2 problems. The contacts where the wiring harness plugs into the tach in back may need to be cleaned up. Pop it off and clean up all the contact. If that is not it, check the switch position on the back of the tach (there is a different setting for 4, 6, and 8 cylinder engines). Yours may be set wrong.
Speedo: If it's stuck, water may have gotten into it, froze and spun the gears. Check if it's a Faria gage and if so, send it back for repair. In 4 weeks and for little cash you will have a working gage. https://faria-instruments.com/forms/?form=new
Trim and tilt issue: If you turn your outdrive all the way so the prop is pointing to the left side of the boat you will see a ~ 2-3" diameter black/brown trim sender with 2 Phillips head screws holding the cover on. This controls the trim gage. perform the following checks:
1) Inspect the 2 wires running to the sender (based on the age of your boat I would assume the insulation is cracked/broken or the wires are gone. If this is the case you need new trim/tilt senders (~$100) which requires a bellows replacement (more $). If they are in good shape, move to #2
2) Remove the cover, pull the printed circuit board disc out and inspect the contacts and disc. If the disc is wiped, you can get a new one from your dealer for ~$16 http://www.marineengine.com/newparts...FUlN4AodTwq3Cw
For the tilt interlock, turn the outdrive completely to the right and repeat #1 above. If the wires are in good shape, move to #2.
2) Remove the cover, inside is a slightly different setup. Pull the disc with contacts out and inspect the contacts on both the disc and inside the tilt sender. Clean them up with emery paper and reassemble. If you can still only trim up with the trailer button, move to step #3.
3) Apply copious amounts of WD-40 to the trim switch on the throttle.
I have done all these personally on my boat and they are all easy do it your self projects.
Lastly, have you had the impeller changed out yet? If not, I recommend doing it sooner rather than later.
Good Luck and let us know how you made out!