Wickes do a taper edge plaster board that does what they call dry wall in the states you fill the edges and screw holes they have the info in the shop it makes a nice job and not expensive .Just change the electrical boxes to plaster board type .Then use a french cleat system to fix what ever to...
First thing i would do is back off all blade guides check them for free running and run the m/c then check bearings in the main wheels with blade removed so the belt drive and motor are the only items left.
My local hire center did mine thursday to thursday service £10-£12 all three but worth obtaining a set from axminster to cover sharpening or damage situations, may be best to hold further adjustments to after new blades.
Blades need to be sharpened all the same to keep block in balance.
As mentioned previously are the blades sharp and sticking out of the block the correct amount. I remember trying to thickness some maple with poor blades it did not like any depth of cut one bit .
This is difficult, from the pictures it look like there is a bush or bearing missing which must be from new or there would be bits of it to be seen is it offset to be able to adjust the chain tension. Actually i think you are in the best position with the components in front of you to resolve...
Here is a link to the manual
http://www.stapeley1.plus.com/manual_aw106pt.pdf
You should be able to check as you describe .When the side cover is off you will see that the main drive has a clutch connected to the drive lever and a number of reducing gears to feed the wood via the rollers check...
Check for debris stoping the action of the spring mechanisms for drive and smooth rollers just lift to check also contamination of them.
The m/c seems to drive harder on the side nearest the removable cover.
I have just purchased a old engineers drill startrite mercury, no play in the quill etc but no rack to raise table and move belt for speed change it was the accuracy i wanted, it was on ebay at half the price of the record.
Read into the subject lots of books on amazon most from usa i have sheds & garages gives some build techniques and design considerations. Actually its a big subject when you think of all the shapes and sizes types of cladding, insulation etc.
My SIP 10'' table saw has a 2200w (3hp) motor that has to run of a 16a dedicated supply as it takes out 13a fuses on start up so i do not think you want to go higher than 3hp.
Insulation contains trapped air chip board does not.What ever you do will be a compromise try a 8x4 sheet of say 2" polystyrene tight up to the metal and look for any condensation at the bottom of that sheet if ok or you can get it away compleat the job and use the chip board as a lining...