Hello and welcome.
As someone who bought a van last year that I knew would need work (is needing work) these are my thoughts.
1-Do as much prior research as you can. Can you check the vehicle history online?
2-Go through it from end to end and make a list as you go, so you can use these points to negotiate on price. Ask lots of questions. When I inspected mine I took a 3T trolley jack and enouigh tools to test all I wanted. If the seller is evasive be especially cautious. Compared to modern vehicles these are quite simple and robustly made vehicles, but for their time they were quite complex and often highly spec'd.
3-Decide what your red lines could be and be prepared to walk away.
4-Have you space (plus tools, money and time) to take it off the road and fix issues that might arise? It's a 30y old vehicle after all and even if it looks mint, there will be 'issues' even if it's been well looked after.
5-If you can, take someone else who can hopefully be more objective.
HTH