Three and a half hours should be plenty of time to collect your bags, change terminal (short bus ride)and check in again. But be warned, Ryanair will be merciless if you are late - if you plane from DTW is seriously late, goes tech. etc. well then you've a problem... you might consider an interline ticket instead, just to be sure?

Also, Ryanair can be savage about the weight of your baggage (16kg), and can be pretty inflexible about the weight of your hand baggage (5kg). If you're one of those travellers who brings a giant roll-on on-board, well you may have a problem.

What can you expect on board? A seat

Not a pre-assigned one either. No food, no drinks, maybe a smile. All craft are 737, of various varieties. If memory serves, LGW is served by 735s (open to correction).

Have a good trip.