<is it possible to install a TK-50 tape drive into the MicroVAX I? I have

Yes, assuming the box has room and the power supply can hold it.

<one of those somewhere, and I also have a RD-54 disk.. shouldn't these b

To use a RD54 you must have a RQDX3 controller, the older RQDX2 will not 
talk to it.

<enough to get it to run some VMS version? afaik OpenVMS 6.1, which is

OpenVMS 6.1 will likely not fit in an rd54 with much free space if any.
I doubt it will run on a microvax1, as support was dropped many years 
(and versions) before. Try openVMS 5.2 or 5.4, it's smaller and may still 
have support for microvax1.  I know VMS4.7 did!

<free for hobbyist use, will run on it. but, is it possible to install
<TK-50 in order to get the VMS installed?

The tk50 can be installed.  Remember the cpu is braindead and also the 
boot roms may not support TK50, try it and see.

Allison