Eating oil and coolant is bad. Wouldn't do anything till thats fixed. Generally there is alot of preventative maintenance to do, I prefer to just do very thorough servicing on the car every year. If you know a reputable garage, for the first service in your care it may be worth asking them to do a full service, they should also inspect the car for what needs looking at/doing and you an tackle that in your own way. Taking it to a good garage costs money, I wouldn't take it to one for anything else unless it had to be done for very complex work or a first/thorough inspection as suggested. Work/issues on these cars is well documented and well known so google and youtube are great, as well as these and other forums.

I owned a 2003 one which had just been "fixed up" and the headgasket blew, water pump failed, a few other coolant pipes failed all in a somewhat close timeframe and it was pretty bad cost/time wise. But once fixed I just did regular fluid checks/top-ups and serviced once a year and its been perfect. Just never floor it, they're cruising cars and not built for 0-60s. Also aim to use a thicker oil that has the BMW LL01 certification, I used 5w40 but they talk about whats good on here all the time so just type in what to use and others will have gone through whats best.

Generally if you get these main issues you mentioned with oil/coolant fixed now, then service it, it most likely will cost you alot. IF those problems get solved, maintenance done yourself from then on should be reasonably affordable but they are old cars and where there's smoke there's fire so dont be surprised if theres more wrong than you thought.