Things I would sort first is the blowing manifold. If it is left too long that can cause some nasty damage and it won’t seal up easily again, esp if its blowing at the block. Its not a big job to get sorted mind.
The drop links and wishbones is the sort of thing you would do all at once. Again they are not difficult, you can get decent enough quality parts off ebay to do the job yourself if you are competent enough. I think you can get all 4 (2 x upper 2 x lower) for around £120 if you shop around in the right places. You need to be doing all these arms at the same time and the drop links will typically be replaced at same time as well. Be sure to get the wheel alignment adjusted once done though, to save ruining any tyres.
Radius arms are another suspension part on the rear of the car, they are not too expensive although again you’re gonna want the alignment checked after its done. Its not major again though.
The radiator I wouldn’t worry about unit it either starts to leak or overheat. Provided your car is running at normal temp, i.e getting up to just short of 90 degrees then its fine. If its only getting to around 50-70 degrees its not getting warm enough and your thermostat is dead, in which case the thermostat and rad will need replacing.
Confused by what is meant about rear main seal, does he mean an engine part or does he mean around the car body / boot / doors?
If its an engine part then that needs to be priority 1 along with the fannymould.
1999 156 1.8TS Sport Pack 3
2001 166 3.0 V6 24V Super
2003 156 GTA 3.2 V6 24V
2005 156 1.9 JTDM-Jet Sport
2008 159 1.9 JTDM Lusso
1997 GTV 2.0TS Lusso
2001 147 1.6TS Lusso