fuji,
your scenario doesn't describe partial panel. that is when you loose your vacuum instruments, ie DI and AI. in that case your workload is much higher.
taking your scenarios though,
first, make sure you are above MSA. if not then full power and pitch the nose about 5 degrees up and climb. then, turn on your pitot heat as it sounds like this has iced up .
if you have a working radio then request assistance and vectors for the nearest SRA or PAR unit. this should be your first request. let someone else worry about your tracking and leave you to the difficult task of flying the thing in a straight line
just follow their instructions. they will give you left 10, right 20 type heading corections. so, remembering compass turns, it's either 3 seconds rate one for 10 degrees, 6 seconds for 20, so on. for rates of descend, try counting to 6 and seeing how much height you've lost. times this by 10 and you have a RoD.
now, if you dont have a working radio, then climb above MSA (if not there already) and make you the beacon overhead. set 7600. if you have file a plan and have given an EAT for the overhead, then thats when you start your approach. before you get to the beacon, check your compass heading and work out how long you need to turn to get on the outbound heading. at the beacon, turn onto your outbound heading. hold wings level and ball centred and check against the compass. wait. after about 2 miles outbound, you will begin to see whether you are left, right or on the outbound radial. the tricky part is to stay on the outbound radial or localiser. don't chase the needles and if you start to drift left or right then turn 10 degrees or three seconds) the other way, level the wings, check the ball and wait. you will then see either the radial/localiser move back towards the centre in which case, once the radial/localiser is centred, then a small turn back should help keep on the outbound radial or centreline.
the base turn will normally require a turn of about 210 degrees. so thats about 70 seconds at rate one. start the base turn and stopwatch. roll out on your expected heading and wait to see the effect on the localiser. again, if you're left, then turn right 10 degrees, wait and see the effect. once happy with your heading/tracking and reasonably well established on the localiser, then drop the flaps, set a lowish power and pitch the nose down about 2-3 degrees. check your not below heights on the profile and try and descend the aircraft as quickly and safely as possible. calculate and check your RoD. at 90 kts you want about 450 fpm for a three degree approach, however, the quicker you get down to MDA the better as once you are visual, the drama ends. of, and i would use the published MDA, not any of the IMC rating add 200 ft to your MDA nonsense.
if you don't have a radio and any radio navigation gizmos, then it is indeed a bad day for you. personally, i would climb to MSA, head due east for at least 90 minutes (fuel allowing for this of course). this should put me over the sea, then descend at a low RoD. the problem with this is that I would have no idea of the QNH over the sea so I would probably wind off 10 millibars from the altimeter as a fudge factor. hopefully you will get visual with the sea before you hit it. then turn back to blighty, and land at the first field you find.
i'm not saying it will be easy but it shouldn't be impossible. just don't panic and if you're not at all sure then climb the buggah back to MSA.