The bolt that you are trying to put in is one of the 2 slider pins. One is on the caliper, one is on the bracket. The two slide into the female part simultaneously. They should be greased lightly.
There is no need to take them off. I have never taken mine off in all the years of owning 4 Pans (UK here).
But it may have thread lock on it. If so, the resistance you are feeling is probably the old threadlock. Stick the bracket into a pan of boiling water and leave it for a few minutes - the threadlock will go all soft and stringy and can be cleaned up with something like a toothbrush - or maybe even a clean bolt.
(on the ST1300, one of the pins requires threadlock, the other doesn't). Check a reliable source.
The rubber boot will need to be replaced - asap. It will work for the time it takes to get a new one, but do not overcompensate by packing the hole with grease (silicone grease). It will lead to brake drag, very hot calipers, and blue tinged discs.
No. Don't ask me how I know this.
Put the slider pin back in (with new thread lock if it requires it - not the permanent sort), torque it up - you may need to mount it on the axle with the stopper bolt in place temporarily to hold it in place while you tighten.
Next thing is to remove the pad pin (I think) - its a long time since I worked on an 1100, but I seem to think its not possible to get the wheel in with the pads in place in the caliper, without doing some damage. Certainly not on the 1300 - but I may be wrong about that - as I say - it has been a long time.....
When you torque up the slider pin, check the torque setting carefully. It will probably be of the order of 23Nm or 27Nm (23Nm is 17 Ft lb. The reason I mention this is because the artist who labelled the diagrams in my ST1300 manual confused the slider pin with the Caliper bracket stopper bolt (the big beggar), which on the ST1300 has a torque of 69Nm/51 ft lb) - which would strip the threads out completely if applied to the slider pin.
Note the figures are what I have for the ST1300. ST1100 figures may be of a simialr value, but they are not the same. Check them out for yourself please.