Ich, as well as some other nasties, are capable of sitting and waiting for your fish to become stressed or have lowered immunities for any number of reasons. At that time, the opportunistic little crud-monkeys pop out of the gravel and wreck havoc in a tank.
You can eliminate many of the lurking parisitical problems by eliminating gravel. They will have the minimal places to hide - and any place they are, you can reach with salt or meds. Many meds and salt do not reach down into the depths of gravel allowing nasties to hide there.
When you stir the gravel up, as in a tank change, you can bring the lurking nasties to the surface, also.
Since you have the time, you can do one of several things....
Buy a filter you would like to use on the new tank now. Set it going on a large tub or bucket and do a fishless cycle on it. It will be finished and set to go come Christmas. Just remember to feed it every day or two.
OR: You can buy a filter that you would like to use on the new tank, now, but set it running in your old tank. (you most likely will need and want multiple filters on a 55 - but you only need to buy one, now) Ich or not, parasites or not, you can get the new filter well cycled and containing a nice colony of beneficial bacteria by running it on your cycled tank right now. When you get the new 55 gal. tank, set it up (no gravel) and move the filter over to it and set it going. DO not move any fish at this time. Feed the filter with ammonia for 2 weeks. This will starve out most of any parasites that you may have inadvertantly brought over in the filter. When you move the fish, do a salt dip to strip the slime coat and any adult parasites they may have off, then transfer them directly to the new tank.
If you feel the old tank is still contaminated, you can then do a 2 week starving in that tank, feeding it ammonia for a bit and leaving it empty of fish. Then move the next set of fish over.
This should minimize the problems that you may have. It will not do it all, but should take care of the majority of anything you may be dealing with!
Sounds like it will be a great new tank and a whole bunch of fun to set it all up! I hope you will share pictures when you do it all!