As a GM I'd remake the characters presented in the modules. RMFRP tends to increase OB significantly, especially if everything is allowed and I've seen 5th lvl PC nearing 100 OB. This was not possible in RM1 or 2. It does even out at later levels between RM and RMFRP.
I'd seriously look at a lot of the creatures presented and the ones that will be used should get an overhaul as well.
To keep things more in check, I'd look over the Vault-downloads section and check out some of the House rules there. Mine are filed there somewhere...
On the story department: use the wonderful background stories and homebrew from that vantage point. Campaign modules never gave much in the way of ready to run adventures so unless the adventures presented are right up your alley, you'd better be a little creative.
I agree fully with kevinmccollum: I'm playing in Endor (and even went into the Dark Continent) for almost all my RP years and my players, even though I try to come up with great alternatives, always choose to go back there. I learned much from the modules and especially from prof. Tolkien's writings. I feel the MERP style is a great interpretation of Tolkien's :" other hands, other minds" statement.
I should note however that it does not always follow canon and real scholars cringe when you start quoting from them.
Also I should be putting in a good word for the Shadow World modules, which are in the same Depth, scope and finish as MERP, with the added benefit that this world will more easily cope with really high level Player Characters. (15th lvl +)